computer aided cartography

Computer-Aided CartographyAuthor(s): David RhindReviewed work(s):Source: Transactions of the Institute of British Geographers, New Series, Vol. 2, No. 1,Contemporary Cartography (1977), pp. 71-97Published by: Blackwell Publishing on behalf of The Royal Geographical Society (with the Institute ofBritish Geographers)Stable URL: http://www.jstor.org/stable/622194 .Accessed: 26/07/2012 11:26

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Computer-aided cartography DAVID RHIND

Lecturer in Geography, University of Durham

Revised MS received 15 September I976

ABSTRACT. Though beset by problems of definition of terms and duplication of effort, computer-aided cartography has progressed over the last 25 years from producing almost uninterpretable assemblages of alphabetic symbols to having the facility for creating any desired graphic image. Two main strands may be distinguished in this development: the 'research' and the 'topographic' cultures. Recent developments, mainly in the provision of data, and the need for sophisticated data-base management software, are forcing these two groups to become increasingly interdependent and fused.

Numerous benefits have been hypothesized for introducing computers into map-making processes: these are reviewed, together with the results of practical experience. The methods and equipment used to date and likely future enhancements are also discussed in relation to the needs of different user groups.

THE definition of terms has become something of an obsession in cartography in recent years and computer-based techniques have provided another impetus to international codifications (I.C.A., I973). More specifically, significant emphasis has been laid by geographers (e.g. Waugh and Taylor, I977) on the existence of a substantive difference between 'computer cartography' and 'automated cartography'. The first of these is used to denote a process for producing essenti- ally thematic-type maps, typically research products, while the latter is viewed as a process involving the use of a computer to produce existing-type topographic maps. Such a distinction is a convenient one, based upon the procedures used to date, the initial sources of innovation and the sparse availability of topographical data in computer form, but it is ultimately a dangerous and misleading one which obscures the identical nature of data handling in both 'fields' at the machine level and the considerable overlap of the subject areas. Thus, for the purpose of this paper, 'digital mapping' 'automated', 'computer' and 'computer-aided' cartography and 'computer mapping' will be treated as synonymous terms, particularly since no satisfactory entirely automated cartographic process yet exists.

With very rare exceptions (e.g. Tobler, 1959), few geographers or cartographers were actually involved at the outset of computer mapping or, less surprisingly, of computer graphics generally. The first successful attempts to produce graphics from computers were reported in the early I950S. By the middle of that decade maps were being produced on the now-standard computer output device, the line printer (e.g. Dobrin, 1952; Inst. of Met., I954; Simpson, 1954), on the earliest cathode ray tubes (Doos and Eaton, I957; Sawyer, 1960) or on tabulating equipment (Perring and Walters, 1962). Both then and now, meteorologists (Menmuir, 1974), geologists (Sampson, 1975), geophysicists, geochemists (Webb et al., I973), plant ecologists and other earth scientists have been the major innovators and users, though a significant growth in use by central and local government planning staff has occurred over the last 5 years (Gaits, 1975) and most national survey organizations in developed countries have at least carried out some experiments with automated mapping. By the end of the I96os the SYMAP program, created by Howard T. Fisher and developed at the Laboratory for Computer Graphics and Spatial Analysis in Harvard University (Schmidt and Zafft, I975), was running at more than Ioo sites. By 1975 this number had grown to 300; since the majority of these sites were universities, this represents a considerable growth in the availability of automated mapping facilities to academics in general.

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Though comparatively recent, these and subsequent developments have not gone un- recorded: by the end of 1975, more than 3000 articles (many in mimeograph form) had been published on different aspects of automation in cartography (K. H. Meine, 1976, pers. commun.) and a Commission of the International Cartographic Association devoted to the subject had been in existence for five years. A growing number of higher degree theses (e.g. Connelly, I968; Degani, I970; Brassel, i973; Kadmon, I973; Tomlinson, i974; Waugh, 1974 and Thomas, 1976) have been substantially orientated towards the conceptual or the technical problems of creating maps with the aid of computers. In terms of financial investment (though the figure is only a crude estimate), no less than ?20 million have been spent on the development of computerized systems for map production, mostly by sections of national government such as the United States defence organizations or national survey organizations, together with others such as the Natural Environment Research Council in the United Kingdom and the Canada Land Inventory: the real costs of these developments could easily be an under-estimate by an order of magnitude or more. Only in the period since I972 have many commercial companies become heavily involved in this field but, even so, it is clear that automated cartography is a topic of wide practical and conceptual interest-far exceeding the realm of academic geography. This generalization obscures many of the important differences between the developments in research and in production institutions. In understanding why automation has been regarded as at least potentially important to so many groups, we must begin by considering (in so far as they are known) the requirements and existing procedures of the two end points of the map-making fraternity-the research worker (occasionally a geographer) and the professional cartographer- then turn to consider the impact of computer processes on these and on the map user in general.

MAP MAKERS AND MAP USERS

Both groups-research worker and professional cartographer-create maps and make use of them in all three possible functions: as a data store, as a data display and as a data-linking mechanism, such as the link between soil memoir and ground provided by the soil map. In many other respects, however, the requirements, aims and resources of the two 'cultures' are very different. The research worker is frequently interested in creating a 'one-off' or 'few-off' series of maps to examine some research finding. Though such maps are sometimes re-drawn for publication, they tend to be monochrome and linework-dominated. The professional cartographer, however, will often see map-making as an end in itself and, in the United Kingdom at least, is most often employed to draw medium- to large-scale topographic maps to an unchanging specification or to plan their production. In the extreme case (the Ordnance Survey) more than 95 per cent of all separate map sheets produced are at i: 10 560 scale or larger (Harley 1975), are designed for litho printing and are completed using many of the new photo-mechanical techniques described by Keates (1977). Though there is a heavy reliance by academics on the professional cartographer through the use of topographic maps for teaching purposes and, more indirectly, by other research workers through the use of topographic base maps as under- lays to geology, soil, land use, slope and many other maps, the indigenous map forms produced are currently very different in appearance, gestation period and means of production.

It follows, therefore, that the defects of present mapping facilities also differ in so far as these different map producers are concerned. To many research workers, especially in universities, the major difficulty of map making is probably the limited availability of sympathetic cartographers who will be able to create acceptable maps from rudimentary sketches and brief conversations. In addition, the ability to experiment with different presentations, extremely helpful in such under-defined design situations, is often highly limited because of the scarcity of draughting resources. Other difficulties for research workers arise in the production of small-

72 DAVID RHIND

Computer-aided cartography scale 'thematic' maps, often complicated by the need to use existing map projection graticules (re-centring a projection or otherwise parameterizing one to be optimal for a specific task is highly time-consuming (see Maling I973)). Finally, in an increasing amount of academic research (particularly that based on government sources), the raw data are already in, or are quickly converted into, machine-readable form; use of manual-based cartography therefore introduces an extra stage into the work schedule.

For the professional map maker, typically in a government-financed institution, the primary requirements are normally high accuracy and speed of throughput, with the mainten- ance, but not necessarily publication, of up-to-date detail. Thus the Ordnance Survey (1975) provides large-scale plans in printed form and also more up-to-date mapped information through microfilm in the SUSI (Supply of Unpublished Survey Information) system. A major problem with cartographic up-dating in a conventional manually based system is that addition of detail to a master copy eventually necessitatesre the re-draughting of the storage document, that is the map, and this is labour-consuming and error-prone. A second problem is that innovation of improved or additional graphics is often delayed by the need for compatibility with the maps previously produced at the same scales, since the older maps cannot normally be made available in the new form. As an example, the only occasion in the o inlast 15 years when Ordnance Survey felt it possible to make significant changes to the graphic form of the one-inch map was when producing the I: 50 ooo scale maps for the whole of Great Britain. These were published in only two separate phases, rather than their publication being spread over many years in which case one inch and I: 50 ooo scale maps would have co-existed.

For the community of map users, the conventional, printed-on-paper map has two over- riding advantages: convenience of use through its ease of handling and dense storage of information; and its low unit costs and ubiquitous nature relative to present alternatives. But set against these are many important disadvantages. One is that the paper map suffers from being scale- and window-immutable: apart from the use of insets, it is not possible easily to change thethe scale of part or all of the map, to move from synoptic to detailed viewing, while it is also impossible to avoid a situation where items of interest are placed at the edge or corner of general purpose map sheets. Further, there is still a lack of agreement on what type and detail of information is really required on 'thematic' maps (see McGrath and Kirby, 1969; Beckett, Tomlinson and Bie, 1972; Salichtchev and Berlyant, 1976) and a paucity of information on what is preferred and needed on topographic ones for different purposes (Drewitt, 1973; Klawe, 1973): because of this and the traditional method of data storage in map form, the map user is usually faced with more information than he needs for his specific purpose and separating the items of interest usually requires manual tracing from conventionally produced maps. Other problems for the user of these maps are legion-map projections often have undesirable characteristics for specific individual tasks. While low in unit cost because of pricing policies and government subsidies, the real cost of producing high-quality cartography by manual means is considerable, particularly if complex photo-mechanical procedures and multicolour printing are required: in one United Kingdom multi-colour maps series, for example, it costs at least Lio ooo to carry out the drawing for and the printing of a run of perhaps 3000 copies, each copy being sold at Li, the stock lasting as long as 20 years for some areas. The longevity of life of such print runs, allied to the high cost of up-dating the information and bringing this to the attention of clients, ensures that many such published maps are long since out of date and frequent pressures are exerted to raise prices to commercial levels. A final and conceptual (but important) disadvantage of conventional map forms is that they are variable pass filters-in a general purpose map, small features may be generalized out of existence or suffer a change of form on re-symbolization, but the effect of context (as in the 'oasis syndrome') and artistic licence ensure that the map user can never be

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really sure of the comparative validity of what he is measuring or reading even within one hand-produced map. Though this comment is particularly apposite in regard to hand-contoured maps of conceptual surfaces derived from haphazardly distributed sample points, it is also applicable in more subtle fashions to topographic maps. Provided the map user is informed of the 'rules' used in compiling a computer-produced map and of any subsequent hand re- touching, he knows what may safely be compared.

HYPOTHESIZED BENEFITS AND DISBENEFITS OF COMPUTER-AIDED CARTOGRAPHY

Several cartographers have regarded the introduction of automation to their field as no more than another change of tools. Indeed, it has been argued convincingly by a senior staff member of the Hydrographic Department of the Admiralty (I. Kembers, 1975, pers. commun.), that the introduction of computerized plotting of chart graticules and ornament has had less effect than the

changeover a decade ago from pen and ink-based drawing to scribing. The alternative viewpoint emphasizes that, since automation can now improve cartographic products over a wide range of

applications, can produce map products which were hitherto impossible, and has also resulted in quite new skills being needed by cartographers, it is best regarded as a revolutionary rather than evolutionary event. The Meteorological Office in the U.K. is one institution which has

successfully pioneered the very rapid production of automated maps for production purposes, to the extent that it is now difficult to conceive of the possibility of wther forecasting without such aids (Menmuir, I974).

Over the period from the announcement of the Oxford System for automated cartography (Bickmore and Boyle I964) until 976, some or all of the following benefits of cartographic automation have been hypothesized by numerous authors (e.g. Littlepage, 1969; Bickmore, I971; Nordbeck and Rystedt, 972; Gaits, 1975; Stutz, 1975; Radlinski, in A.C.S.M., I976, p. 4; Bickmore et al., 1976):

i. To make existing-type maps more maps more quickly. Superficially, an increase in speed of mapping for automation would seem inevitable, especially when one considers, as an example,n the numerous socio-ecnomic studies and maps of the United Kingdom which appeared between I968 and 1974--based on the 1961 Census of Population. In the circumstances where the statistics are provided by a well-organized branch of Government, and where their format is known in advance, suitable mapping and manipulation programs are already available (Coppock, I975; Rhind, i97Cb) and a single location is given to reference a small data area, then maps can be produced by computer of, say, as many as ioo variables within a week of the receipt of data. Most of this week is likely to be consumed in human decision- making-in assessing class intervals (Evans, 1977) and in checking the output for any data errors or map specification errors-and thus human, rather than computer, resources may set the upper limit to what can be achieved.

Considering 'topographic cartography', a speed-up in production would also seem to be an easy task since even the current high-accuracy, electro-mechanical plotting tables can draw complex maps at around i to 2 cm/sec. Such an increase in the speed of production of topographic maps is highly desirable in many parts of the world. Even in a highly developed country like the United States, some 21 6oo00 of the 54 00ooo 7-5 minute quadrangle, I :24 000 scale maps required to cover the lower 48 states were not published in 1973 and, of the published ones, some 8oo000 were in need of revision (Radlinski in A.C.S.M., 1976). Similarly, Canada (Harris, 1972) has a recently completed coverage at I :250 000 scale but it will be many years before full coverage at I: 50 00ooo scale is available. The contrast between the speed of hand drawing which was used to produce such maps and that of the second generation of plotters is extreme: as a

74 DAVID RHIND

Computer-aided cartography

consequence of their modes of operation, they can often plot at around oo times the speed of the more traditional plotters (though, as yet, their output quality is not as high as that of the best flat-bed plotters with optical projectors) and perhaps Iooo times the speed of the average draughtsman. Unhappily though, plotting time is often only a small part of the gestation period of high-quality, multicolour maps. Data compilation, checking, editing, proofing and the constraints of organizing a work flow through the drawing office and factory can compose up to

90 per cent of the time required to create printed maps (see Keates I974). Where only low- to medium-quality results are desired, it is possible to plot results extremely

rapidly on graphic terminals: maps containing 2000 point symbols (graded squares) have been generated and then plotted by the author in about 20 s on a Tektronix 40I4 storage cathode ray tube or C.R.T. (see Fig. 2) for a computer-determined cost of $I.20. This elapsed time is related to the available communication facilities and plotting could in theory be reduced to around

0-05 s. As yet, plotting of this kind is not available in colour; though colour cathode ray tubes do exist, their resolution and capacity are very poor in comparison with the monochrome competi- tors. Clearly, then, not all present-type maps can invariably be made much more quickly by automated means. Only when three conditions are satisfied-that the data are already in digital form, that they are for simple fixed-size and shape areas (such as i km squares) or for areas where boundaries are already digitized, and where the maps may be presented in monochrome on cathode ray tubes or on a computer line printer-can very rapid production of maps be guaranteed.

2. To make these maps more cheaply. Costing the production of maps is a complex matter, only possible over an extended period of time. Such costing is further complicated by introducing computers into the mapping. Since the amortization of software and of computer time varies greatly from institution to institution, evaluation of benefits is particularly difficult. In the environment of a British university, computing can produce free mapping facilities since computer time is sti ll (in 1976) an internally free resource. Further, if only ephemeral maps (drawn on cathode ray tubes or other similar displays) are produced, it is difficult to maintain a meaningful record of exactly what has been produced and how it was used. In the United Kingdom, however, simple video terminals are already the same price as typewriter terminals and do not consume paper: the cost benefits are even more marked between graphics terminals and colour-printed maps, so it is a reasonable supposition that their use and therefore costing difficulties may increase still further in the future.

An alternative cost-based justification for computer use in cartography has been advanced in relation to the editing of large volumes of line and boundary data. Using either simple batch mode editing (Gardiner-Hill, 1972) or interactive editing (Bickmore and Bell, 1975; Sippel, 1975;

Kroll, 1975), only those map elements which are in error or out of date need to be replaced, minimizing the work of the operator who should never need to redraw (or digitize) more than a very small section of the 'affected' map. The cost justifications for this are (at the time of writing) unproven, but may well grow if the data are suitably organized (see below) and given the con- tinuing diminution in costs of computer hardware in contrast to the rising labour costs.

Perhaps the most common cost-based justification is the spin-off provided by digitizing once and yet having the possibility to produce maps at different scales by merely re-plotting the results: the tenet is entirely based on a presumption of low plotter costs in comparison with those of the rest of the cartographic process. Though some of this was demonstrated long ago (Cobb, 1971), the most striking example to date is the production by Ordnance Survey of 1/1250,

1/2500, i/io ooo and 1/25 000 scale maps from the same digital data base; the publication of

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two Herefordshire I/Io ooo scale maps in late 1976 as new forms of the standard map series emphasizes that this is more than technical virtuosity. More extreme scale reductions than this do, however, rapidly encounter severe problems of generalization (Rhind, I973; Stewart, I974). Automated capabilities for generalization are slowly improving (Lang, 1969; Boyle, 1970; Douglas and Peuker, 1973; Gottschalk, 1974), but, in any case, it is far from invariable that published derivative maps differing only in scale from the original publication are required from the same data.

3. To produce maps whose content is related solely to the user's needs. If no unequivocal and universal advantage for automation can yet be seen in terms of cost, the benefits for selection of detail are very real given the disadvantages of conventional maps which have already been enumerated. Sheet edges become transparent to the user who has his own plotting facilities-thus he can specify any area of interest for which data are stored in machine form, whether that area is a rectangle super-imposed over the junction of four map sheets or a highly irregular polygon, and still get maps made to meet his requirements. In addition to

specifying such geographical criteria, the user can specify attribute criteria, for example 'only plot those houses where the rateable value is greater than 300o per annum' or 'plot all those regions where the out-migration is greater than io per cent over the last io years'. Such selection facilities may well depend on the data having been suitably classified before encoding, but the

ability to select features and then to treat the world as being an infinitely extensive plane which may be sampled at any point are basic to almost all automated cartographic facilities: they are invariably of value to 'research-type mapping' and in the production of maps of networks, such as of power lines of different voltages. In addition, they are episodically of great potential im-

portance to map-making institutions because they would minimize problems of re-draughting caused by a change of sheet lines.

4. To make possible map production in situations where draughting and basic skills are becoming scarce in relation to demand. Some institutions in London, for example, were under-staffed in their drawing offices between 1970 and 1974 because of an inability to recruit the necessary skills at permitted salary expendi- tures.

5. To facilitate experimentation with differing graphical representation of the same data. Though our knowledge of what is effectively perceived in maps is not yet extensive (Board and Taylor, 1977), much of the graphic symbolism now used in cartography is not based on good evidence that it is the 'best' means for conveying the information. There are known advantages of familiarity with graphic symbolisms but the cost of trying alternatives often prohibits experiment: in an automated system the costs of producing alternatives should amount to little more than the cost of re-running a plotter and such a cost is trivial if the plotter is a cathode ray tube. Hence graphic experiments are greatly facilitated if suitable equipment and comprehensive software are available. It is also worth noting that perception experiments in cartography are both difficult to arrange and evaluate: as controlled experiments, they demand numerous map forms which differ from one another in no more than one aspect. Automated mapping facilitates the production of the test material of this kind.

6. To facilitate map making and up-dating when the data are already available in digital form. In the United Kingdom and the United States at least, much mapping may be carried out from data already stored in digital form. By mid-1976, more than 00ooo plans were available on mag- netic tape from Ordnance Survey. The Agricultural Census (Coppock, 1976), the Census of Population (Rosing and Wood, 197I; Coates, I974; Shepard, Westaway and Lee, I974; Dewdney

76 DAVID RHIND

Computer-aided cartography and Rhind, 1975; Gaits, 1975), the Census of Distribution and the yearly'Regional Statistics'

published by the Central Statistical Office are some United Kingdom examples of mappable data available in or trivially converted to machine form (see also E.C.U., I97I). At a regional level, most health authorities have growing data bases which describe variations of various kinds in illness incidence and vaccination efficacy. Crime records are also typically automated. Un- fortunately, the different files are frequently structured in different ways so that cross-referencing, for example between agriculture and industry in an area, is not simple. None the less, there are still increasing tendencies in the United Kingdom and elsewhere in Europe to provide some form of spatial reference on each item and, if all else fails, this can be used not only to map the individual data files but (usually) to cross-reference one file with another. An extreme example of file linkage of geographically referenced data in this way is the work of Rokkan and associates at Bergen, who have assembled data for I2 ooo variables relating to 440 communes covering the whole of Norway and who are extending this to cover the period from I837 to I975 (Reve, I975; Rokkan, 1976, pers. commun.).

7. To facilitate those analyses of data which demand iteration between statistical analysis and mapping. Much of the work previously denoted as 'statistical cartography' has involved calculations prior to the mapping; the production of frequency distributions and univariate statistics to aid decisions on selection of class intervals is one such example. Such analysis has been limited in the past because of the difficulties of making mechanical computations by hand or by machine and then manually mapping the results. Now, however, it is entirely possible to carry out some statistical exercise, map the results, carry out a more refined statistical exercise suggested by the results, map the new results ... etc. This type of iterative analysis, particularly where done interactively at a computer terminal, can greatly speed analyses and such integrated capabilities are likely to become very common over the next decade since an obvious need exists for them in research environments. Similar analytical facilities may well become common in 'topographic cartography' since, for example, it is helpful to have some prior knowledge of the total number of points or line length in a map section which is to be plotted, in order to estimate plotting time; it is also valuable to know the sinuosity characteristics of lines in deciding which generalization method to apply. Parenthetically, it is notable that, at the present time, we still have rather few quantitative concepts of what maps contain by way of length of line, number of point symbols, etc. (but see Tienstra and van der Kraan, 1975); estimates of computer storage space required for maps, such as that a typical I :24 00ooo scale U.S. Geological Survey map requires about ioo00 million bits of data storage (Roberts, i962, Radlinski, in A.C.S.M., 1976, p. 4), are not very helpful since this is highly dependent on the data compaction techniques utilized (see Amidon and Aiken, 1970; Vaniceck and Woolnough, 1975; Visvalingam, 1976).

8. To minimize the use of maps as data stores. Though heavily criticized by Robinson and Petchenik (I975), studies of information theory applied to maps (Sukhov, 1970; Balasubramanyan, 1971) have at least shown that these can act as extremely dense stores of 'information'. However, though compact, this method of storage can give rise to problems of retrieval or up-dating. For example, in some countries-particularly those without a national cadastre-many maps are used primarily to store such information as the distribution or location of power cables, sewers and other underground networks and wells. In areas of rapid change the maps have to be up-dated frequently and, because of their nature as working documents, re-drawn quite frequently. Every manual re-drawing is likely to compound errors. Storage of the data in digital form ensures that, once correct, the data remain correct and also that the contemporary situation or changes over a given time period may be plotted at will.

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9. To create maps of a kind which are extremely difficult or impossible to produce by hand e.g. on certain map projections or stereo maps (Adams, I969; Laughton, Whitmarsh and Jones, 1970; Sampson, 1975).

io. To create maps in which the selection and generalization rules are explicitly defined and

consistently executed.

1. The introduction of automation, especially in bureaucratic institutions, often necessitates a

thorough review of how and why existing maps are produced; this in itself can lead to substantial economies.

Where the innovation of computer use for map production comes from an individual researcher in a university, little is wasted other than his time if the application proves un- reasonable. In corporate bodies, however, a number of practical experiences have revealed disbenefits. Few organizations or individuals have yet written on any aspect of the difficulties encountered in implementing automated systems, except where they are explicitly justifying the need for an improved system (e.g. Gaits, I975). The following list of disbenefits is therefore based on informal discussions with more than 50 staff members in major North American and European centres:

I. To get an initial commitment of funds, promises of rapid results have frequently been made. Few automated cartographic systems are yet production tools and virtually no experimental system has worked either as efficiently as promised or in less than twice the originally estimated period. Much duplication of effort has occurred, some of which is evident in I.G.U. (1977).

2. The acceptance of computerized methods and the acquisition of equipment and staff make any subsequent return to manual methods almost impossible. Each enhancement of the system often seems essential to obviate bottlenecks created by a

previous enhancement, that is computerizing the work produces a positive-feedback system. In addition, the more flexible any production cartographic system has to be in terms of producing different maps forms, the more difficult it is to arrange that the existing equipment is efficiently used at all times. Experimental systems often seem to make use of some pieces of equipment for less than 10 per cent of the time available.

3. Only in very restricted circumstances can existing systems yet be shown to be cost-effective. (cf. Pfrommer, 1975, and above).

4. There is a danger of producing new maps because the facility is there and is easy to use, rather than because these maps are needed. A few of the now-numerous atlases produced from census data using SYMAP seem to fall into this category.

5. In a situation in which the technology and available software are changing rapidly, selection of the most suitable equipment and programs is a difficult management decision. The unit cost of computing power had dropped to approximately 2 per cent of its I963 cost by a decade later and the advent of microprocessors and networked links between computers holds out promises of considerable savings in the future. Unlike computer central processors, the costs of plotting and digitizing equipment have not decreased over the last I 0 years, but their productivity has increased by as much as o00 per cent in some circumstances. Current developments in

plotting and (especially) digitizing equipment could produce considerable further gains in

throughput for the large-scale user in the medium term.

78 DAVID RHIND

Computer-aided cartography 6. A major staffing problem may arise since computer personnel are often better paid than traditional cartographers. Not only do different salary scales produce administrative problems, but the admixture of very different types of personnel may give social problems.

7. The spin-off benefits envisaged may not arise-if for no other reason than a lack of user knowledge of what is possible.

Some of these points will be taken up in more detail later: sufficient has now been said to indicate that the use of computers is potentially (and sometimes in practice) a powerful aid to production of different kinds of maps, but that the advantages are sometimes illusory and that the overall planning of implementation and use of any system is critical if it is to be successful.

DETERMINANTS OF MAP QUALITY AND FORM

The concept of quality in map terms is extremely difficult to define (and thus measure) but may be exemplified by the multicolour map of many different zones, allied to clear typography, comprehensive legend and aesthetically pleasing appearance. In practice, quality need not mean accuracy in any absolute sense: geological boundaries are often shown in their correct position relative to a hand-generalized topographic underlay rather than to the 'correct' position given by a photographic reduction of a large-scale map. There appears, however, to be a wide con- sensus that the line printer produces low-quality mapping. Perhaps 90 per cent of all the maps yet produced with the aid of automation (certainly those published in the geographical press), have been produced by line printer (see below and Fig. 3). To this extent, 'computer maps' have become identified as instantly recognizable assemblages of different alphabetic characters, creating a picture through density variations. Yet this is quite misleading, since at least as long ago as I97I it was demonstrated that high quality maps indistinguishable from hand-made products could be produced by computer-based means (Rhind, I97I). Coppock (I975, p. I53) has argued that 'fuzzy maps' are quite adequate for 'fuzzy data' but, even if acceptable, this contentious point should not obscure the availability of the technical means to produce by machine any type of map yet produced by hand.

In any local circumstances, the determinants of what may be achieved in mapping by computer are combinations of the following:

i. The spatial reference or notation used to locate the spatial individual (see Deuker, 1974; Waugh, 1974; Pfaltz, 1975; Rhind, I975a). High order spatial referencing, such as that by zonal outlines for data areas, is much more flexible than lower-order referencing, such as the single-point gle-point co-ordinate: many more forms of graphical representation are available for the former than the latter (except in the special circumstances where zonal boundaries are st neighbour criteria). Whether all possible forms may be produced does, of course, depend on the equipment available locally. The lowest level of spatial referencing, represented by a postal address, is a nominal one on spatial measurement scales and can only be mapped sensibly by reference to some other external information such as the co-ordinates of street end-points. The quality of zonal-type maps is related in part to the accuracy and the resolution of the boundary co-ordinate strings: boundary data encoded by digitizing machine are therefore likely to produce much higher quality output than those produced by manual encoding.

The special case of grid cell mapping (Dewdney and Rhind, 1975) ensures that an appar- ently low-level spatial reference (point co-ordinate) may be used to produce highly accurate maps. Grid cell mapping causes complications on all except very special line printers (Coppock,

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I975), because the standard print characters are rectangular. Cells are often printed as assemblages of 5 x 3 printing characters and the resulting large maps are photographically reduced in size.

2. The response rate and quality demands of the users. Variations in response-rate demands are enormous, from the desire for instant displays from the research worker using a terminal or after a natural disaster to those of the users of geological and similar maps for teaching purposes. It has already been pointed out that high throughput of maps can be produced rapidly only under certain circumstances; high response rate is sometimes even more difficult to achieve, particularly if the request was unforeseen by the system designer.

Demands for higher quality output may be met by simply driving a plotter more slowly or by photographic reduction of size of output. If this is not feasible (and the latter destroys the advantage of final-size output) recourse to commercial plotting services may be necessary.

3. The volume (Tomlinson, I974) and organization of the data (Peuker and Chrisman, I975; Visvalingam, 1975). A line printer map of the i-km grid square 1971 population census statistics of Great Britain would be a minimum of 3-35 m high by I-8 m broad. Use of a standard line printer would increase this size to about I6 m by 9 m if equal scales in X and Y axes were retained. Such volumes of data are thus not suited to normal facilities and, if no other equipment were available, mapping could only sensibly be carried out after aggregation of the data to larger areal units. The organization of large data sets is also critical in determining whether selected variables or areas can be retrieved and mapped within the computer resources available (see section on Geographical Information Systems).

4. The type of output device available (see below).

5. The sophistication of the available computer programs. Far more computer programs are available in the literature for line-printer mapping than for use on pen or C.R.T. plotters, though the reverse is probably true of commercial suppliers.

6. The constraints of design inertia, either through a legislated need to maintain comparable, country-wide cover or through satisfaction with the existing product. In this respect it is striking how closely the Abingdon and Swindon one-inch geological maps produced by the National Environment Research Council's Experimental Cartography Unit for the Institute of Geological Sciences and the United States Defence Mapping Agency's map of Shiraz reflect their conventional map specifications for these scales of maps.

THE MECHANICS OF AUTOMATION

Only digital devices will be considered in this section, though Thomas (1976) has suggested that analogue displays may be very useful for map depiction and were, in any event, used widely by the Meteorological Office until recently. It is helpful to consider the mechanical aspects of automation in cartography under four sub-headings: data capture, checking and editing of the data, retrieval and manipulations of them and data display. These are convenient sub-divisions but do not describe exclusive categories: for instance, one frequently used checking method is to plot the data so as to overlay them on an existing map; encoding the data through digitizing and

editing them are also firmly linked in many systems (e.g. see Boyle in A.C.S.M., 1976). Figure I

illustrates a simplification of the process involved in computerized map production. Only the most common feedback loops are shown: thus checking and editing are shown as an iterative

8o DAVID RHIND

Computer-aided cartography 8i

Capture Checking and editing Retrieval and manipulation Display

> I > remote listing/plntting 8 visual checks- map image creation raster vector (surrogate) + V sensing automated arithmetic and--

logical checks plotter ehemeral A plo?er !

ephemeral A

tactile I aptans definitive sensing kv multi-element association

A or comparison (eg overlay)

historical [ geographic editing > 1

lists Fr . selection on attribute(s)

Lo +

^ attribute editing > map F selectior on area(s) sources

> (master file(s)

reformating, code conversion , etc

Jdata from external sources

FIGURE I. The map production process in a computer environment

process. Since details of the procedures involved are now easily available in the published literature (e.g. see Dale, I974), they need only be repeated in summary form here.

Data capture The first stage normally necessitates the creation and storage of two kinds of description. The first is the location of the spatial unit-point, line, area, volume or hypervolume, in either Euclid- ean space using a grid co-ordinate system or by using geographical co-ordinates. The second involves the assignment of meaning or attribute to the spatial description. In practice, data are often stored in different forms from that in which they are collected in order to minimize the space requirements and/or speed processing (Freeman, I974).

Historical lists of data are commonly handled by research workers and their encoding is simple: a more complex. data source to encode is an existing map. The basic procedures of semi- automated digitizing from such a source were spelled out in descriptions of the Oxford System in I964 (Bickmore and Boyle, I964), but mechanical problems, other technological considerations and economics meant that consistently acceptable semi-automated digitizing of maps was not available until circa I971. In principle, the digitizer operator guides a cursor over the feature to be encodi d and co-ordinate pairs defining it are generated by the machine (often every tenth of a second) and stored, together with descriptive information entered via a typewriter, a menu or by other means (Rhind, 1974b). Significant problems encountered in the large-scale use of this technique include the large volume of data collected, the slow rate of digitizing (commonly of the order of i m of line per man/hour for freehand work on complex lines), line-following accuracy and distortions in the source document which lead to overlap or underlap of data plotted for adjacent map sheets. Careful operational procedures can minimize many of the problems and the many possible errors at an early stage, but even the use of on-line editing procedures, in which a small computer is linked to the digitizing table to screen data, check on operator actions, trans- form co-ordinates directly from table to grid form, etc. (Kroll, 1975; Sippel, 1975; Moritz in A.C.S.M., I976, p. 68) cannot catch all errors.

Attempts to remove at least the human, guiding process from this form of digitizing have been made since at least I966: only recently have these been crowned with any real success in digitizing of multi-colour maps or of complex line work. The close juxta-position and intersection of lines in complex fashions, allied to the common use of pecks and broken lines for symbolization and the presence of background 'noise' such as names, have created a much more complex engineering task than that for the lock-on digitizers used in bubble-chamber photograph digitizing.

None the less, recent successes (Wohlmut in A.C.S.M., I976, pp. 118-26) have indicated that such automated line following can be highly successful in economic and accuracy terms, especially if there is a high throughput of similar material in feature-separated form to be digitized. Ryan (in A.C.S.M., I976, p. 102) has indicated the value of on-line forms of flying spot scanners in digitizing globally related line work such as contours.

A quite different approach to the encoding of mapped data was pioneered by the Rome Air Defence Centre of the Defence Mapping Agency in the mid-g1960s (Diello, Kirk and Callander,

I969) and even earlier by the Canada Land Inventory (Tomlinson, I967; Switzer, 1975). This involved the scanning of printing plates or feature separations in such a way that the map was broken up into black or white (or, at Rome Air Defence Centre, into coloured) squares about o-i mm across and the image stored as a raster. In most linework-based maps, the result was an inefficient encoding since a very high percentage of the separation was white and the continuity

consuming and complex task. The method has the advantage, however, that much of the digitizing operation is entirely automatic, extremely rapid and independent of the amount of data on the

map. It is suited for high-throughput, constant map-form uses where the separations are already available, no functional meaning needs to be given to any symbol (encoded as a series of un- related black or coloured squares) and where a large computer is available for processing. Changing graphic form between input and output is often difficult with the resulting data, in contrast to the situation where the basic stored data elements have a functional context, for

example an 'atomic line segment' might be that section of the centre of a river which also formed an administrative boundary.

Tactile and remote sensing are extreme points on a scale of contemporary data collection which is increasingly becoming automated. Environmental remote sensing, in particular, has

undergone dramatic developments in the last decade in terms of tasks successfully accomplished, variety of sensing platforms, resolution of sensors and the extent to which the returned data are

directly machine-ine-interpretable and capable of automated mapping. Estes and Sengar (1974), A.S.P. (I975), Collins and van Genderen (1975and nd Bernstein (1976) give useful introductions to the field. Petrie (1970) and others have questioned the utility for mapping of much of the smaller scale imagery obtained from earth satellites, but Calvocoresses (1975) and many others have presented results which indicate the value of such imagery for non-altimetric semi-automated mapping. Wang (1974) has pointed out that I0 m contour interval maps at 1/2000 scale have been made of lunar areas from imagery obtained by a satellite 46 km above the moon, while Batson and Dwornik (1974) have demonstrated extremely striking computer-enhanced photomaps produced from digitally stored data. Armstrong and Brimblecombe (1975) and many others have demonstrated that it is possible to go directly from the digital tapes of the LANDSAT

multi-spectral sensor data through classification procedures to produce interpretable qualitative- unit maps (the LANDSAT imagery is repeated every i8 days and each scene covers an area

approximately i85 km square, being built up of reflectance values for cells 80 m across, the volume of digital data being 7-6 x io6 bits per spectral band per scene). The value of automated or semi-automated interpretation and subsequent mapping of such massive data sets is obvious,

82 DAVID RHIND


particularly since recent studies have made it clear that much more can often be extracted by machine and subsequently plotted than is possible by visual interpretation of the simple 'photographs' plotted from the totality of the data.

One, more traditional, form of remote sensing which has become partly automated and has had some impact on cartography is that based on stero-photography, leading normally either to the production of a stereo-compiled traditional line map or to an orthophoto map (see Petrie, 1977). Partial automation of the former has been effected by replacing the normal plot output from a stero plotter by shaft encoders and thus producing digital descriptions on tape. For the geomorphologist and highway engineer, the direct, digital terrain model output from a scanning orthophotoscope is a valuable spin-off from the orthophoto mapping process and is easily mapped as slopes or altitude. Though obtained from small-scale sources, altitude data coverage of the entire United States now exists and the coverage elsewhere is growing: it is at least conceptually possible to produce maps from combinations of this and satellite data.

Checking and editing spatial data In a cartographic context, editing can be distinguished from up-dating since many data used to produce maps are archival: once error-free, they are never deleted, only supplemented. The possible checks and editing mechanisms for spatially distributed data are given in Rhind (I974b, I975b) while numerous acconts of methods are given in A.C.S.M. (I976). n most cases, checking and editing is found to be an iterative procedure: not all errors can be detected or removed in one phase and, in addition, changes to the data sometimes produce new errors. The growth in availability of cheap computing power has ensured that the more checks which can be made by machine, the more cost-effective the re thediting process will be, but certain checks-such as the exactness of positioning of the centre portion of a line segment-can only be checked by reference to the source document. Checks which can be made by machine are that no part of the digitized map is outside a specified window, that no codes or attributes are present other than those expected by the operator and that boundaries of zones do actually close.

In editing map-source data only a restricted number of general functions are required (Rhind, 1976), such as 'delete', 'move', 'join' and 'add' feature(s); the system design is thus straightforward. In conceptual terms, the mode of working is unimportant-the same functions are used whether in a batch mode (Gardiner-Hill, 1972) or in editing at an on-line terminal. In practice, increasing use is being made of interactive editing facilities for reasons of convenience and because they tend to introduce fewer new errors in operation. However, a frequent problem with the editing of data such as geological boundaries on C.R.T. terminals (as in Fig. 2) is the lack of displayed topography to act as a framework for moving lines and zones. Some data sources, such as satellite-based imagery, are difficult to check and edit: indeed.such data are often regarded as not needing to be checked or edited by the user, following use by the data supplier of such sophisticated digital correction procedures as those described by Bernstein (1976).

Retrieval and manipulation of data Until circa 1971, most automated cartographic systems used the simplest possible means of retrieving their data-sequential reading of the totality and rejecting what was found to be outside the specified geographic or attribute window. While this was simple, it also meant that certain tasks readily carried out by the map analyst or by a human cartographer, such as working out- wards in a given direction through a street network, could only be achieved by frequent rewinding of tapes or other devices and reading the data set many times. In its most extreme form, this method of access would have ensured reading all variables for all areas on a tape of census-type information in order to obtain a value for one variable in the last area. Clearly this is an absurdly

83

DAVID RHIND

FIGURE 2. Using a high-resolution Tektronix 4014 storage cathode ray tube

simple means of organization of the data and is now obsolescent. However, since the organization of large volumes of geographically distributed data for tasks which often produce mapped output and the availability of computer software to achieve complex retrieval are inherent parts of recent developments in Geographical Information Systems (I.G.U., I972; Tomlinson, I974), this element is left to a later section for discussion.

Forms of manipulation which should be considered here include the specific task of interpolation of surfaces through haphazardly distributed points in space and the creation of the digital map image-both achieved by transformations of the notation used for the data. The problem of producing surfaces is not a new one and indeed was one of the earliest attacked by computer-orientated earth scientists. Though some conclusions in the K.O.X. (Kansas Oil Exploration) project suggested that better results could be obtained by machine rather than human interpolation (W. A. Read, I974, pers. commun.), this cannot be regarded as a general conclusion since many qualitative and quantitative data elements cannot be built into the vast majority of existing computer packages (Barrett and Rhind, I975). Peuker (1972) and co-workers have devoted much effort to the structuring (Peuker and Chrisman, I975) and presentation of

84

Computer-aided cartography TABLE I

Types of digital output device

PLOT MODE raster vector

alpha- storage ephemeral numeric tube or

C.R.T. refreshed IMAGE C.R.T. PERM- ANENCE line flat bed

printer; or drum definitive Dresser/ plotters

Seiscom plotters

85

surface data, but it remains clear that the major problem is obtaining a 'likely' as opposed to 'possible' surface from the data. Though it can be argued that surface generation is not a cartographic problem, it has important side-effects for map making, since the type of digital description of surface can influence the graphic symbolism used, for example where triangulated procedures are used for contouring, some indication should be given of which data points formed the triangles, permitting a visual check on stability of the results. Rhind (I975b) has reviewed the surface interpolation methods available, but the autocorrelation-based Universal Kriging method (Delfiner and Delhomme, I975) seems to offer the most satisfactory approach for many, though not all, applications. In principle, surface interpolation is an under-defined problem in machine terms, in contrast to change of scale or map projection and most other automated cartographic procedures.

The creation of a map image is an important step since, as Rhind (1976) has argued, a plotting file which can be sent to any plotting device which is available-be that a colour microfilm plotter or a line printer-is an essential element in modularity of future cartographic systems. Without this, the map creator needs an intimate knowledge of the vagaries of each kind of plotter; this is an undesirable characteristic if the facilities are to be easily used. In some instances map image file creation is a trivial problem involving only a change of data format. In others, it is far from trivial-particularly if it is essential to draw raster-organized data as lines on a vector display (see below).

Data display The previous section indicated that the type of output device was a severe constraint upon output quality. The types of digital output device may be classified as in Table I. The raster plotters produce map images by area filling: thus the line printer is the crudest commonly available raster plotter, though computer typesetters have also been pressed into unintended use for mapping. Figure 3 is a line-printer map produced with special symbolism at the University of Edinburgh and, in original form, is almost as good as could possibly be obtained by this method (see Coppock, 1975; de Gruijter and Bie, I975; Stoye, 1975). Rapid strides in technology have produced a variety of other raster plotter mechanisms using electrostatic, ink jet (Smeds, 1973), electron beam or laser (Rhind, I974a) technology. One of the most sophisticated is a 5o-micron resolution plotter produced by Seiscom Ltd. for plotting maps on up to sixteen different intensi- ties over a metre wide and infinitely long sheet of film. Ephemeral raster-type maps are very

LEGEND VALUES ARE GROUPED IN 6 GROUPS

0.000 0.422 1.154L 2.751 5.681I 10.197 l 47.711 FREQ. ( 64) ( 64) ( 61) ( 63) ( 63) ( 65)

FIGURE 3. Line-printer map of horticulture as a percentage of tillage in England and Wales by Agricultural Advisory District. Source: Agricultural Census

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DAVID RHIND

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rarely produced, the most common reason for their creation being the sole availability locally of the standard alphanumeric video display unit: in such use, the display mimics a line printer.

The mode of action of vector plotters in drawing lines as lines, rather than as filling very thin areas with tiny squares, is much more akin to the human draughting process. A variety of forms of vector plotters exist, from the crudest ?3000 drum plotters in which pen movement across the drum and drum rotation combine with pen up and pen down commands to give positional movement (see Figs 4, 5 and 6) to the ?Ioo ooo, high-accuracy, flat-bed, electro- mechanical plotters with optical projection of symbols on to photographic film (Figs 7 and 8). The latter can be typified by the Calcomp 7500 which has a granite plotting surface to ensure

stability. For cartographic purposes much the most frequently used ephemeral map vector display is the storage cathode ray tube, in which the image is drawn once and stored on the phosphor of the tube. Until 1974 this was only available in a small ( 5-cm square) format image area but the introduction of the 38-cm square Tektronix 40I4 was an important advance (see Fig. 2). Many other displays are now available of this type, of which the most interesting is perhaps the HRD

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Computer-aided cartography 89

I\ 11 I

FIGURE 6. The concentration of boron on the island of Unst (data provided by Geochemical Division, Institute of Geological Sciences and published by permission of the Director)

I laser plotter, which can produce either ephemeral or permanent images (Street and Woodsford, I975), has a I-m screen, the same interaction capabilities as a storage tube and has a io bit intensity modulation facility, that is it has the capability to produce continuous tone images like photographs, normally on microfiche.

Some use has been made by geographers and cartographers of refreshed displays such as the IMLAC, in which the image is re-plotted many times per second and continuity of perception is ensured by the operator's visual persistence. Though these offer the ability to change images instantly, they are more demanding of computer resources than are storage tubes and the current speeds of plotting, allied to the normal volumes of cartographic data, ensure that flicker and breakdown of the image occur frequently. It is important to note that all vector plotters can, in theory, be programmed to act as raster plotters, though operationally this may not be successful. It is neither theoretically nor practically possible to use raster plotters as vector ones.

Most plotter manufacturers provide plotting packages which the user can incorporate in his computer programs to drive the plotter in simple fashions. Many such packages include the facility to draw up to 50 or so special symbols but, to go beyond point symbol and simple line plotting and plot re-scaling, the user generally has to provide the bulk of his own computer software unless it can be obtained through a software exchange scheme (such as the Geographic Program Exchange based in Michigan State University). A good example of the variations in graphic form which are feasible in a computer-based system where the data storage and depiction are not inextricably linked and where special purpose software has been written is in the depiction of surfaces by Brassel, Little and Peuker (I974), Batson, Edward and Eliason (I975) and Yoeli (1976). They have produced contoured, inclined contour, Tanaka-style, slope vector, hill-shaded and other forms of surface portrayal. Currently, some of these demand exotic and rarely available equipment, but standard contouring is now a frequently used and simple technique (see Fig. 5).

DAVID RHIND

o o 3

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FIGURE 7. High quality linework from Ordnance Survey i: 1250 scale plan SU 4114 SW plotted using a Ferranti

age of data which are only related indirectly to geography. The objection may be pedantry, but the term describes a rapidly growing field of interest, stemming from the late 1960s and early 1970s, which saw a rapid growth in the computer-based information system business. The primary customers were and remain local administrative authorities and large commercial and manufac- turing firms, which typically have the requirement to handle large volumes of data at a very disaggregated level and are able to assess and/or update any part of this quickly and efficiently. The environmental equivalent of this development was the growth in popularity of the environmental inventory; the business/computing-type approach to such inventories was epitomized by the creation circa 1962 of the Canada Land Inventory and its technical arm, the Canadian Geographic Information System (C.G.I.S.; see Switzer, 1975). Academic interest in the field in

90


FIGURE 8. High-quality output from World Data Bank II plotted using a Gerber plotter with photohead (provided by the Central Intelligence Agency)

the United Kingdom was minimal until circa I970, with the formation of B.U.R.I.S.A., a British version of the Urban and Regional Information Systems Association. The most significant overall formal step in the involvement of academic geographers in the geographical information

system field was the formation of the commission on 'Geographical Data Sensing and Processing' of the International Geographical Union. The success of this commission is evidenced by their influential publications (Tomlinson, I97I; I.G.U., 1972; Tomlinson, Calkins and Marble, 1976; I.G.U., I977) and the large grants given by state and federal agencies in the United States to the Commission for the investigation of information systems for land-use planning and for the review of data-base developments in the U.S. Geological Survey.

The implications of all this for automated cartography are very substantial indeed, since those individuals involved in the use of the spatially referenced data bases have long since begun to make maps in increasingly large numbers. Though production of lineprinter maps is very

9I

common from such systems, the maps produced from this source have never been restricted to the low-quality type: C.G.I.S. was designed from the outset to cope with input from high- resolution maps and the facility for output of answers in moderate and high-quality map form was soon added.

Several distinctly different lines of development can be discerned in work to date. One of the earliest and computationally simplest methods (see Boehm, I967; I.G.U., I972) was to store data for spot locations or for fixed-size and fixed-shape areas. Examples of information systems based on single point locations are the property centroid-based Joint Information System for Tyne- Wear County (N.G.P.S., 975) which contains 600o000 land-use records, and the similar, if smaller, Durham Land Use Survey System. In the Minnesota Land Management System (Hsu, Kozar, Orning and Street, 1975), grid cells (in reality, the 40-acre parcel) were used as the basis for data storage because this is the 'atomic structure' of Minnesota's landscape, it is the basis on which many governmental records at county, regional, state and federal levels are based and because it also lends itself to computer mapping. The New York State Land Use and Natural Resources System stores land use and topographic data by i-km squares. Similarly, Duffield and

Coppock (I975) have built a system which uses 5 km and i km square-based data for Scotland and use this to produce maps of the output from combined logical, arithmetic and geographic searches on several variables: 'map all the locations with more than 50 empty hotel beds in

August within 5 km of water more than 5 km2 in extent' is the form of request which would

normally be serviced. Perhaps the largest grid-based data set extant, other than the LANDSAT satellite output, is the I50 ooo record by I67I variable Great Britain I97I Census of Population (the data are also made available by Enumeration District areas). The creation of an information system to handle this, involving the compaction of the data into one-tenth of its original volume and speeding the access to the whole data set by a factor of thirty over the standard procedures, has made access to any part of the data possible within a few seconds on an on-line system and, as a result, has made possible the production of a large variety of computer maps. A more sophisticated system operating with variable-size grid squares is the ORRMIS system, devised at the Oak Ridge National Laboratory (Tomlinson, Calkins and Marble, 1976). LINMAP, a United Kingdom government-created Geographical Information System designed to produce statistics and point symbol, zone and grid maps after retrieval and combination of data from various government sources, has been in use since about I973 and has been described by Gaits (1974, I975). In that time it has been used to produce over Iooo maps.

A distinctly different line of development includes schemes such as the PIOS system (Dangermond, 1972; Tomlinson, Calkins and Marble, I976), GIMMS (Waugh, I974) and NIMS (B.U.R.I.S.A., I976), which are often segment-based systems. In the latter, street or other physical and conceptual boundaries are assembled in chains to create networks or zones. The most widely used segment-based scheme is undoubtedly the Dual Independent Map Encoded-or DIME-file, originated by the U.S. Bureau of Census (U.S. Bureau of Census, I970), even though the original DIME file did not permit the segments to be other than straight lines. While much more demanding to collect than are point-or grid cell-referenced data, these facilities do provide the possibility of some automated data quality checking (Aangeenburg, I975), which is virtually impossible in point-referenced files. Availability of such zonal outlines permits the simple automation of choropleth mapping: perhaps the most striking cartography yet produced from such files is that by the U.S. Bureau of Census (Meyer, Broome and Schweitzer, I975) in the 65 atlases of those Standard Metropolitan Statistical Areas with a population over

500 ooo in 1970. To produce these, 5000 colour separations for 780 maps were produced in a

14-month period. It has been pointed out in a previous section and emphasized above that the variations in

DAVID. RHIND 92


sophistication of the spatial reference have significant effects upon the final map form. In an information system context, however, the manipulative operations which it is possible to carry out (Tomlinson, I974; Rhind, I975b, 1976) partially determine the map content and these are critically related to the organization of the data elements and their implicit and explicit cross references. Peuker and Chrisman (1975) have suggested that most existing cartographic data files are input-related, i.e. their organization is a reflection of how the data were digitized or otherwise created. In addition, they emphasized that comparatively few attempts have been made to link geographical data files together (but see U.S.G.S., 1975): as a result, quantitative com- parisons of the relationship, say, between geology and soils (Tobler, I975) is extremely difficult. Finally, Peuker and Chrisman (1975) pointed out that most data structures used to date for cartographic files only include topology in an implicit way. There is now widespread recognition of the necessity for inclusion in files of what they summarize by 'flexibility, comparability and topology': a good example of the effects of the lack of these in an initial system is the difficulty in use of the Ordnance Survey digital map data (Atkey and Gibson, 1975). In this, data were initially stored more or less as they came off the digitizing machine, in a way designed to simplify the re-drawing of existing-type maps. One major disadvantage of this method of storage is that it is impossible simply to generate functional units such as properties, since a house frontage is stored as some part of the side of a street while other parts of the boundary of the same property are not related to each other in any explicit way and are usually scattered throughout the file. The start of a major project, which is intended to produce the means for software reorganization of the data as required, was largely brought about in I975 by the inability of potential users to relate their own data to that of the Ordnance Survey and thus save themselves digitizing the same boundaries as those provided by the national survey organization.

It should be appreciated, however, that the requirement to carry out many different operations with cartographic data ensures that the data organization will be extremely complex. The example given in Rhind (1976), which contains a vast miscellany of pointers to permit direct access to individual and related data elements in an extremely simple map, is not an atypical structure. In addition, the use of such cartographic or geometric data for logical or arithmetic tasks such as polygon overlay necessitates rather higher standards of data quality than have been necessary for such mapping in the past: it is quite one thing to fill in missing sections of a plotter- drawn line by hand but quite another to compute areas if some part of the boundary is missing. In some cases, therefore, the data accuracy requirements differ for cartographic and analytical purposes.

CONCLUSIONS

The development of automation in cartography has largely followed two different courses until recently, related to the involvement of research workers, such as geographers and (more often) earth- and social-scientists on the one hand, and 'topographic cartographers' on the other. In essence, all the substantial and solvable conceptual problems in map making have been solved through the individual efforts of these groups, though not all of the solutions have yet been documented and the pre-display operations of generalization and surface generation will remain problems since they are under-defined. The multiplicity of world-wide developments in the field suggest that any type of map extant can now be produced by making use of a computer, though the sensible degree of involvement of the machine will depend on local facilities, labour availability, economics and the time-scale of the project. The most obvious present benefits of automation come when the data are already in digital form and when large numbers of similar- style maps are required or where progressive up-dating is to be carried out. However, the growing availability of both 'topographic' and 'thematic' data in digital form and of appropriate software

93

94 DAVID RHIND

and hardware suggests that user interaction with the map form and personalized production of maps will grow in importance.

The next major benefit of involving the computer in the production of maps, however, is likely to come through the increasing use of sophisticated data-base management techniques to obviate redundancies in the data set and to link different and hitherto incompatible data sets together so that derived variables can be mapped and analysed. The latter is far from an easy task, particularly in the United Kingdom where different data sets are collected over areas of

many different sizes and shapes. But economic pressures are already forcing the 'topographic cartographers' to find other users for their data while, at the same time, academics and government 'thematic cartographers' are beginning to appreciate the potential of readily available

digital maps for linking with their own data or for use merely as a backdrop to them. An ironic form of this co-operation is the use by numerous geographers (and others) of the C.I.A.-produced World Data Bank I (Robe in A.C.S.M., 1976, pp. 152-62) and the eager anticipation of the much more detailed country boundaries, rivers and railways in World Data Bank II (Fig. 8). For these reasons, and in this one respect, the gulf between the research and the professional cartographic cultures seems now to be diminishing.

ACKNOWLEDGEMENTS

Thanks are due to the Central Intelligence Agency, Ordnance Survey, Dr S. M. Scarrett and Mr T. C. Waugh for kindly providing some of the illustrations. Mrs J. Dresser typed all the drafts of the paper.

REFERENCES

AANGEENBURG, R. (1975) 'Computer graphic editing of urban maps: a topologic classification of urban polygon files', in WILFORD-BRICKWOOD, BERTRAND and VAN ZUYLEN, op. cit. 1-9

A.C.S.M. (1976) Proc. int. Conf. on Automation in Cartography, I974, Am. Congr. Survg Mapp. ADAMS, J. M. (1969) 'Mapping with a third dimension', Geogrl Mag. 42, 45-9 AMIDON, E. L. and AIKEN, G. S. (I970) 'Algorithmic selection of the best method for compressing map data strings', Communs

Ass. comput. Mach. 14, 769-74 ARMSTRONG, A. C. and BRIMBLECOMBE, P. (I975) 'Rapid digital mapping of coastal areas from LANDSAT', Cartogr. 7. I2,

89-93 A.S.P. (1975) Manual of remote sensing, Vols i and 2, Am. Soc. Photogrammetrists ATKEY, R. G. and GIBSON, R. J. (1975) 'Progress in automated cartography', Conf. Commonw. Surv. Offrs, Pap. J3 BALASUBRAMANYAN, V. (197I) 'Application of information theory to maps', Int. Yb. Cartogr. . , 177-81 BARRETT, A. N. and RHIND, D. W. (1975) 'Retrospective application of boundary constraints in automated contouring by

digital spatial filtering', Mathl Geol. 6, 83-9 BATSON, R. M. and DWORNIK, S. (1974) 'Mapping the planet Mars by Mariner 9', Pap. presented to 7th Int. Conf. int.

Cartogr. Ass., Madrid

BATSON, R. M., EDWARDS, K. and ELIASON, E. M. (1975) 'Computer-generated shaded relief images', . Res. U.S. geol. Surv. 3, 40I-8

BECKETT, P. H. T., TOMLINSON, P. R. and BIE, S. W. (1972) 'lap quality: the second St Cross Seminar, Oxford, 1971', Cartogr. J. 9, 8o-i

BERNSTEIN, R. (1976) 'Digital image processing of earth observation sensor data', IBM rl Res. Dev. 20, 40-57 BICKMORE, D. P. (1971) 'Experimental maps of the Bideford Area', Conf. Commonw. Surv. Offrs, Pap. Ei BICKMORE, D. P. and BOYLE, A. R. (1964) 'An automated system of cartography', Tech. Symp. int. Cartogr. Ass., Edinburgh BICKMORE, D. P. and BELL, S. (I975) 'Automatic cartography at the ECU-regional geography a la mode', Conf. Commonw.

Surv. Offrs, Pap. J6 BICKMORE, D. P., CRAMPIN, S., LINTON, R. H. W. et al. (1976) 'A computer-based atlas of seismic activity, 1909-68', Pap.

presented to 8th Int. Conf. int. Cartogr. Ass., Moscow

BOARD, C. and TAYLOR, R. M. (1977) 'Perception and maps: human factors in map design and interpretation', Trans. Iinst. Br. Geogr. N.S. 2, 19-36

BOE-IM, B. M. (I967) 'Tabular representation of multivariate functions with applications to topographic modelling', Proc. natn. Conf Ass. comput. Mach. 22, 403-15

BOYLE, A. R. (1970) 'The quantised line', Cartogr. J. 7, 91-4 BRASSEL, K. (1973) 'Modelle und Versuche zur automatischen Schraeglichteschattierung', unpubl. Ph. D. thesis, Univ. of

Zurich

Computer-aided cartography 95 BRASSEL, K., LITTLE, J. and PEUKER, T. K. (1974) 'Automated relief representation', Ann. Ass. Am. Geogr. 64 (4) Map Suppl.

17 B.U.R.I.S.A. (1976) 'Application of the NIMS segment referenced information system', Br. Urban reg. Inf. Systems Ass.

Newsl. 20, 20-2

CALVOCORESSES, A. P. (1975) 'Evaluation of the cartographic application of ERTS: I. Imagery', Am. Cartogr. 2, 5-I8. COATES, B. (1974) Census atlas of South Yorkshire, Dep. Geogr., Univ. of Sheffield COBB, M. H. (1971) 'Changing map scales by automation', Geogrl Mag. 43, 786-9 COLLINS, W. G. and VAN GENDEREN, J. L. (eds) (I974) 'Fundamentals of remote sensing', Proc. ist Tech. Sess. Remote

Sensing Soc. (London) CONNELLY, D. A. (I968) 'The coding and storage of terrain height data: an introduction to numerical cartography', unpubl.

M.Sc. thesis, Cornell Univ. COPPOCK, J. T. (I975) 'Maps by line printer', in DAVIS and MCCULLAGH, op. cit. I37-54 COPPOCK, J. T. (I976) An agricultural atlas of England and Wales, 2nd edn (London) DALE, P. F. (ed.) (1974) 'Automation in cartography', Br. cartogr. Soc. Spec. Publ. I DANGERMOND, J. (1972) 'A classification and review of co-ordinate identification and computer mapping systems', Pap.

presented to Urban reg. Inf. Systems Ass. Conf. DAVIS, J. C. and MCCULLAGH, M. J. (eds) (1975) Display and analysis of spatial data (London) DEGANI, A. (1970) 'Automatic isoline mapping using computer plotter and isodensitracer techniques', unpubl. M.A. thesis,

Univ. of Minnesota, Minneapolis DE GRUIJTER, J. J. and BIE, S. W. (1975) 'A discrete approach to automated mapping of multivariate systems' in WILFORD-

BRICKWOOD, BERTRAND, and VAN ZUYLEN, op. cit. 17-28 DELFINER, P. and DELHOMME, J. P. (1975) 'Optimal interpolation by kriging', in DAVIS and MCCULLAGH, op. cit. 96-I14 DEUKER, K. (I974) 'Urban geocoding', Ann. Ass. Am. Geogr. 64, 318-25 DEWDNEY, J. C. and RHIND, D. W. (eds) (1975) People in Durham: a census atlas, Census Res. Unit, Dep. Geogr. Univ. of

Durham DIELLO, J., KIRK, K. and CALLANDER, J. (1969) 'The development of an automated cartographic system', Cartogr. J. 6, 9-17 DOBRIN, M. B. (1952) Introduction to geophysical prospecting (New York) p. 336 Doos, B. R. and EATON, M. A. (I957) 'Upper air analysis over ocean areas', Tellus 9, 184-94 DOUGLAS, D. and PEUKER, T. (I973) 'Algorithms for the reduction of the number of points required to represent a digitized

line or its caricature', Can. Cartogr. 10, I 112-22 DREWITT, B. (I973) 'The changing profile of the map user in Great Britain', Cartogr. J. IO, 42-7 DUFFIELD, B. S. and COPPOCK, J. T. (I975) 'The delineation of recreational landscapes: the role of a computer-based in-

formation system', Trans. Inst. Br. Geogr. 66, 14I-8 E.C.U. (I971) Automatic cartography and planning (London) ESTES, J. E. and SENGER, L. W. (I974) Remote sensing: techniques for environmental analysis (Sta Barbara, Hamilton) EVANS, I. S. (1977) 'The selection of class intervals', Trans. Inst. Br. Geogr. N.S. 2, 98-124 FREEMAN, H. (I974) 'Computer processing of line-drawing images', Computg Surveys 6, 57-97 GAITS, G. M. (I974) 'Spatial data recording and processing for urban planning and management', in DALE, op. cit. o108-26 GAITS, G. M. (1975) 'Design and use of the new LINMAP-COLMAP system', in DAVIS and MCCULLAGH, op. cit. 267-81 GARDINER-HILL, R. C. (1972) 'The development of digital maps', Ordnance Survey Prof. Pap. N.S. No. 23 GOTTSCHALK, H. J. (I974) 'Automatic generalisation of settlements, traffic lines, drainage and vegetation boundaries for a

small-scale topographic map', Pap. presented to 7th Int. Conf. int. Cartogr. Ass., Madrid HARLEY, J. B. (I975) Ordnance Survey maps: a descriptive manual, H.M.S.O. HARRIS, L. (1972) 'Mapping the land of Canada', GeogrlJ. I38, I3I-8 Hsu, M. L., KOZAR, K, ORNING, G. W. and STREET, P. G. (I975) 'Computer applications in land-use mapping and the

Minnesota Land Management Information System', in DAVIS and MCCULLAGH, Qp. cit. 298-310 I.C.A. (I973) Automation terms in cartography, Int. Cartogr. Ass. Commn III, published by Cartogr. Div. Am. Congr. Survg

Mapp. I.G.U. (1972) Geographical data handling, Int. Geogr. Un., Reprinted by National Technical Information Service, Spring-

field, Va., I.G.U. (i977) Computer software for geographic data handling, UNESCO INST. OF MET. UNIV. OF STOCKHOLM (I954) 'Results of forecasting with the barometric model on an electronic computer

(BESK)', Tellus, 6, 139-49 KEATES, J. S. (I974) Cartographic design and production (London) KEATES, J. S. (1977) 'Developments in non-automated techniques', Trans. Inst. Br. Geogr. N.S. 2, 37-48 KADMON, N. (I973) 'Automated cartography for the atlas of Israel', unpubl. Ph.D. thesis, Univ. of Wales KLAWE, J. J. (1973) 'A survey of Canadian topographic map users,' Am. Congr. Survg Mapp. Proc. Fall Conv., 148-61 KROLL, F. S. (I975) 'Interactive editing of cartographic data,' in WILFORD-BRICKWOOD, BERTRAND and VAN ZUYLEN, op. cit.

145-65 LANG, T. (I969) 'Rules for robot draughtsmen', Geogrl Mag. 42, 50-I LAUGHTON, A. S. WHITMARSH, R. B. and JONES, M. T. (I970) 'The evolution of the Gulf of Aden', Phil. Trans. R.Soc. Ser.

A 267, 227-66 and accompanying maps LITTLEPAGE, G. G. (I969) 'Computer-assisted cartography', Nachr. Kart.- u. VermessWes. 50, 94-8

96 DAVID RHIND

MALING, D. (1974) Co-ordinate systems and map proiections (London) MCGRATH, G. and KIRBY, R. P. (I969) 'Survey methods on the use of maps and atlases,' Can. Cartogr. 6, I32-48 MENMUIR, P. (I974) 'The automatic production of weather maps', in DALE, op. cit. MEYER, M. A., BROOME, F. R. and SCHWEITZER, R. H. (I975) 'Colour statistical mapping by the U.S. Bureau of Census',

Am. Cartogr. 2, IOO-I7 N.G.P.S. (I975) Memoranda i to 8 of the National Gazetteer Pilot Study, Co-ordinating Committee on Locational Referenc-

ing, Department of the Environment NORDBECK, S. and RYSTEDT, B. (I972) Computer cartography (Stockholm) ORDNANCE SURVEY (I975) The Supply of Unpublished Survey Information (Southampton) PETRIE, G. (I970) 'Some considerations regarding mapping from earth satellites', Photgramm. Rec. 6 (36) 590-624 PETRIE, G. (I977) 'Orthophotomaps,' Trans. Inst. Br. Geogr. N.S. 2, 49-70 PEUKER, T. K. (I972) 'Computer cartography', Ass. Am. Geogr. Commn on Coll. Geogr. Resource Pap. No. I7 PEUKER, T. K. and CHRISMAN, N. (1975) 'Cartographic data structures', Am. Cartogr. 2, 55-69 PFALTZ, J. L. (I975) 'Representation of geographic surfaces within a computer', in DAVIS and MCCULLAGH, op. cit. PERRING, F. H. and WALTERS, S. M. (eds) (1962) Atlas of the British flora (London) PFROMMER, W. L. (1975) 'Cost and benefit considerations concerning computer-aided cartographic systems,' in WILFORD-

BRICKWOOD, BERTRAND and VAN ZUYLEN, op. cit. 3I3-20 REVE, T. (1975) 'Computer mapping for spatially variable data', European Political Data Newsl. I7, European Consortium

for Political Research, Bergen RHIND, D. W. (1971) 'The production of a multi-colour geological map by automated means,' Nachr. Kart.- u. VermessWes.

52, 47-52 RHIND, D. W. (1973) 'Generalisation and realism within automated cartographic systems,' Can. Cartogr. Io, 51-62 RHIND, D. W. (I974a) 'High speed maps by laser beam', Geogrl Mag. 46, 393-4 RHIND, D. W. (I974b) 'An introduction to the digitising and editing of mapped data', in DALE, op. cit. RHIND, D. W. (I975a) 'The state of the art in geographic data processing', in ALDRED, B. K. (ed.) Proc. IBM U.K. Scientific

Centre Seminar on Geographic Data Processing, Rep. UKSC 0073 RHIND, D. W. (i975b) 'A skeletal overview of spatial interpolation techniques', Computer Applications 2, 293-309 RHIND, D. W. (I976) 'Towards universal, intelligent and usable automated cartographic systems. ITC J7, 1976-3, 5 5-45 ROBERTS, J. A. (I962) The topographic map in a world of computers. Prof. Geogr. I4 (5) 12-I3 ROBINSON, A. H. and PETCHENIK, B. B. (I975) 'The map as a communication system', Cartogr. J. I2, 7-15 ROSING, K. E. and WOOD, P. A. (1971) Character of a conurbation. A computer atlas of Birmingham and the Black Country

(London) SALICHTCHEV, K. and BERLYANT, A. M. (1976) 'Methods of map use', given to 8th Int. Conf. int. Cartogr. Ass., Moscow SAMPSON R.(I975) 'The Surface II graphics system', in DAVIS and MCCULLAGH, op. cit. 244-66 SAWYER, J. S. (I96o) 'Graphical output from computers and the production of numerically forecast or analysed synoptic

charts', Met. Mag. 89, I87-90 SCHMIDT, A. H. and ZAFFT, W. A. (I975) 'Programs of the Harvard University Laboratory for Computer Graphics and

Spatial Analysis', in DAVIS and MCCULLAGH, op. cit. SHEPARD, J., WESTWAY, J. and LEE, T. (I974) Social atlas of London (Oxford) SIMPSON, S. N. (1954) 'Least squares polynomical fitting to gravitation data and density plotting by digital computers',

Geophysics 19, 250-7 SIPPEL, J. J. (1975) 'Automated editing of digital graphic data,' Photogr. Engng Rem. Sensing 41, 1047-58 SMEDS, B. (I973) 'A 3-colour ink jet plotter for computer graphics,' BIT I3(2) I81-95 STEWART, H. J. (1974) 'Cartographic generalisation: some concepts and explanation,' Cartographica Monogr. 10 STOYE, U. (1975) 'Herstellung mehrfarbiger Themakarten auf der Grundlage von Schnelldruckerkarten,' Int. Yb. Cartogr.

15, 158-64 STREET, G. S. B. and WOODSFORD, P. A. (1975) 'The HIRD-i Laser Display System', in WILFORD-BRICKWOOD, BERTRAND

and VAN ZUYLEN, op. cit. I84-92 STUTZ, F. P. (1975) 'Interactive computer cartography', Cartogr. J. 12, 17-20 SUKHOV, V. I. (I970) 'Application of information theory in generalisation of map contents', Int. Yb. Cartogr. IO, 41-7 SWITZER, W. A. (I975) 'The Canada Geographic Information System', in WILFORD-BRICKWOOD, BERTRAND and VAN ZUYLEN,

op. cit. 58-8I THOMAS, A. N. (1976) 'Spatial models in computer-based information systems,' unpubl. Ph.D. thesis, Univ. of Edinburgh TIENSTRA, M. and VAN DER KRANN, J. G. (1975) 'Some figures about automated large scale mapping', in WILFORD-BRICK-

WOOD, BERTRAND and VAN ZUYLEN, op. cit. I66-73 TOBLER, W. R. (1959) 'Automation and cartography', Geogrl Rev. 49, 526-34 TOBLER, W. R. (1975) 'Analytical cartography', Am. Cartogr. 3, 2I-31 TOMLINSON, R. F. (I967) An introduction to the geographic information system of the Canada Land Inventory. Dep. Forestry

and Rural Dev. (Ottawa) TOMLINSON, R. F. (I97I) 'Environment information systems,' Proc. UNESCO/I.G.U. ist Symp. on Geographical Information

Systems, Ottawa, I970 TOMLINSON, R. F. (1974) 'The application of electronic computing methods to the storage, compilation and assessment of

mapped data', unpubl. Ph.D. thesis, Univ. of London

Computer-aided cartography 97 TOMLINSON, R. F., CALKINS, H. W. and MARBLE, D. F. (976) 'Computer handling of geographical data,' Natural Resources

Res. Ser. No. 13, UNESCO U.S. BUREAU OF CENSUS (1970) 'The DIME geocoding system,' Census Use Study Rep. 4, Dep Commerce, Washington, D.C. U.S.G.S. (1975) 'Digital cartographic data base preliminary description: a proposal', Off. Res. tech. Standards U.S. Geol.

Surv., Reston, Va VANICECK, P. and WOOLNOUGH, D. F. (1975) 'Reduction of linear cartographic data based on generation of pseudohyper-

bolae,' Cartogr. J. 2, 112-19 VISVALINGAM, M. (1975) 'Storage of the 1971 U.K. Census data, some technical considerations', Census Res. Unit Wking

Pap. 4, Univ. of Durham VISVALINGAM, M. (1976) 'Indexing with coded deltas-a data compaction technique,' Software Practice and Experience 6,

397-403 WANG, K. W. (1974) 'Surveying and mapping from orbital platforms,'J. Surv. Mapp. Div. Am. Soc. civ. Engrs Ioo, I5-31 WAUGH, T. C. (1974) 'Geographic data in a systems environment', unpubl. M.Phil. thesis, Univ. of Edinburgh WAUGH, T. C. and TAYLOR, D. R. F. (I977) 'GIMMS: an example of an operational system for computer cartography',

Can. Cartogr. (in press) WEBB, J., NICHOL, I., FOSTER, R., LOWENSTEIN, P. L. and HOWARTH, R. J. (I973) 'Provisional geochemical atlas of Northern

Ireland', Appl. Geochem. Res. Grp, Imperial College, London WILFORD-BRICKWOOD, J. M., BERTRAND, R. and VAN ZUYLEN, L. (eds) (1975) 'Automation in cartography', Proc. int. Cartogr.

Ass. Commn. 3, Tech. wking Sess. YOELI, P. (I976) 'Computer-aided relief presentation by traces of inclined planes', Am. Cartogr. 3, 75-85

computer aided cartography

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