lecture 4 cartographic process
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8/12/2019 Lecture 4 Cartographic Process
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LECTURE 4
THE CARTOGRAPHICPROCESS
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Cartographic Generalization Concepts
• Map production necessarily involves undertaking
a number of processes which are collectively
described as Cartographic Abstraction.
• This is the process whereby we transformfeatures of the earth onto a map.
• This involves far more than mere or simple
reduction.
• It is an Encoding Process in which the final
product, the map, will become meaningful to the
map user.
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Generalization Processes
• They are logical steps or processes required toachieve cartographic generalization.
• They include selection, classification,
simplification/exaggeration and symbolization.
• By these processes, the cartographer attempts to
portray only the essentials of an environmental
or geographical situation which is defined by the
purpose or objective of the map.• In the process, we often and usually eliminate the
visual complexity of the map by simplifying their
outlines through categorizations
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SELECTION
• The map is necessarily selective since, unlike the
photograph, we cannot include all aspects of reality of theworld.
• The first logical requirement of map abstraction
therefore is to reduce the complexity of the environment
to a manageable number.by using clearly definedguidelines or thresholds
• The map makers’ first job is therefore to select the
information that will go into the intended map.
• Selection begins by setting thresholds or cut-off points in
terms of information or data to be mapped.
• In this first stage the cartographer is guided by questions
based on the following: where, when, what.
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SCALE SELECTION FACTORS
Purpose of the map
Needs of the map user
Map content
Size of mapped area
Maximum font sizeLevel of accuracy required
Etc.
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Factors in the Selection Process
• Purpose/objectives: Since there are various types of maps, decisions made in the selection
process will be guided first by the purpose of the map. The topic and variables to be mapped will beguided by
Physical and material aspects of the environment e.g. topography and hydrology, vegetation,
rainfall and humidity, etc
Non-physical or Human aspects, e.g. Traffic flows, crime and disease
• Region to be mapped: The environment we live in is so vast that it is difficult to obtain a precise
overall picture. The factors that will guide us here include locat ion or localit ies of things to becovered e.g. the whole world or part of it, a continent, country, region or province, district or
settlement.
• Time frame: This relates to current data e.g. yearly or monthly, depending on the objectives of the
map as well as relevance to the map user. In Ghana the most recent topographical maps are dated
1970 and 1990.
• Variables to be mapped: What to include depends on the size or scale of the map; purpose and
available information (e.g. maps for sailors will show cliffs in the sea which ships have to avoid; tourist
maps will show routes and tourist attractions.
• Choice of scale: How to go about reducing the size of our environment to fit the map frame
becomes a most important decision: should the map look at a few things nearby or a lot of things far
away? This consideration addresses one of the concepts in cartography, namely scale. Scale may be
defined as the “ratio of distances on a map, to the actual distances they represent on the ground”.
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Data Collection Method
Direct field observation using compass, chain
or Global Positioning System (GPS)
Sampling & Indirect or secondary methods forgathering socio-economic data from reports,
censuses, interviews and questionnaires
Remote sensing methods involving the use thecamera at various altitudes, platforms and films.
(GEOG 307 – Remote Sensing and GIS)
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Measurement Level • Measurement levels: Qualitative and Quantitative levels.
Qualitative mode: the cartographic data and the symbols for representing
them are merely descriptive, e.g. the position of a road or river. Quantitative mode : things mapped and the corresponding graphic
symbols (points, lines and areas) vary according to numbers or quantities.
• Inventory Scale
Map makers have important choices regarding the strategy used to collect
information to be mapped. These are the population and sample methodology. Population inventory: When this choice is made, every element of the
distribution is taken into consideration, e.g. every tributary of a river,
every city or every small dam
Sample inventory: In this case, only a portion of the distribution or
population is targeted e.g. only selected tributaries or selected cities in the
distribution, or selected small dams
Sample methodology: The sample methodology for obtaining the required
data may be random, systematic, or stratified
• Cost: The execution of mapping operations has obvious cost implications
which can become a very important factor as it may limit the choice of
alternative actions or activities available to the cartographer. As a result, the
cartographer is sometimes in dilemma regarding the need to produce quality
maps at least cost often demanded by clients or map user.
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Since maps are the
transformation of thespherical earth or
parts of it onto a flat
medium like a sheet of
paper, there is need to
understand the basis
and characteristics forsuch a transformation
or projections of
surfaces e.g. cylinder,
cone and plane
/azimuth. Perspective
of the mapped areamay also relate to
aerial photographs
which may be
differentiated as
vertical or oblique
photographs.
A head drawn on the
Mollweide projection(top) has been
transferred to Mercator’s
projection with (centre)
and to the cylindrical
equal-area projection
with standard parallels
at 30 (bottom).
Just because the profile
looks most natural on
Mollweide’s projection,
that projection is notnecessarily “better.”
The natural could have
been drawn on any
projection and then
plotted on the others.
Perspective or
projection
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Classification
• Robinson et. al. (1978) have defined classification as “ the order ing or
scal ing and grouping of data with a view to br ing relat ive order
and simp l ic ity out of the comp lexi ty of incom prehensib le
di f ferences, inco nsequential di f ferences, or the unm anageable
magnitudes of information”.
It is a grouping process where information selected for mapping is
grouped into a relatively small number of categories in order to have a
meaningful map.
Map makers generally classify as a means of reducing the complexity of
the map information so that, for example, instead of showing individual
trees, we can have the following: Forested areas, Non-forested area,
Grassland
Therefore the map maker’s first duty in classification is to decide the
number of classes, depending on the characteristics of the data.
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Classification Criteria/Methods
Point Feature,Line Typification,
Aggregation of Areas, and
Aggregation of Volumes
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Point Feature Methods
Fig 4.1 Illustrations of collapsing process in generalization.
Point feature methods
may result in collapsingof several elements or
features.
This results in obvious
loss of dimension of thefeature being mapped.
We may use this
procedure when we must
group or collapseindividual elements and
specify a typical location
for the group
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Line Feature
Typification
Figure 4.2 Typification by classification of point, line and area features
Indeed, the same principles can be applied to all categories of maps including flow maps showing volume of air,
vehicular movement or traffic during rush hour and off peak hours to work.
This method is applied
to complex patterns
consisting of individual
features as shown inFigure 4.2.
The process of
typification allows us to
retain the essence ofthe pattern on the
reduced-scale map.
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Aggregation of Areas
• This method results in grouping orcoalescing of area units or features.
• It depends on the size of area units being
aggregated and the scale of mapping in
relation to level of detail e.g. land use
classes
(Level I,
Level II,
Level III,
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Number of classes
• Depending on how general a viewpoint
a cartographer takes of the situation,
he can decide to group the data into a
number of classes.
• The choice of few classes for mapping
conceals details whilst a large number
of to overcrowding of information of
the map.
Cl li it
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Class limits• In determining the number of classes, the map
maker must determine the class limits.
• A key question to be considered would be “what
point can one group end and another one begin?”
• This is determined by the cartographer’s objective
assessment and understanding of the data.
• In an attempt to classify, we can have constant
series of class intervals; variable intervals which
may be arithmetic or geometric; or even irregular
classes as shown in Table 1
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Table 1: Class limits.
Constant
Series
Systematically
Unequal Stepped
Irregular/
Variable
1 – 20
21 – 40
41 – 60
61 – 80
81 – 100
Arithmetic
(5n)
Geometric
(5n
)
1 – 10
10 – 15
15 – 18
18 – 30
1 – 5
6 – 15
16 – 30
31 – 50
1 – 5
6 – 30
31 – 156
157 – 782
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SIMPLIFICATION & EXAGGERATION
MANIPULATIONS
• When we undertake cartographic simplification, we determine
important characteristics of feature attributes and, in theprocess, maintain these important features and attributes of the
data and eliminate unwanted details. In doing so, we have two
main objectives:
• We must reduce the amount of information to the map maker’sability to portray it legibly at the chosen scale. At this stage, we
must be guided by how much information to include on the map
• We must maintain as far as possible, the essential geographical
characteristics of the mapped phenomenon
• Cartographers use simplification to eliminate unwanted
information. This is done through two major routines i.e.
elimination and smoothing. The overall objective in simplification
is to avoid overcrowding of information on the map.
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Simplification/Manipulation
Procedures
• Feature elimination (Eliminating
unwanted features)
• Smoothing details out of boundaries
• Measurement level reduction
• Combining or compacting variables
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Elimination routines
• As map scales get smaller and smaller, fewer features
can be represented. Part of the solution is therefore to
select only the features which are necessary to be
portrayed.
• Cartographers achieve this by eliminating some of it
and smoothing (reducing details) of the remaining
feature.
• Scale of mapping is therefore very important as
illustrated in Figure 4.3 (a, b.). Figure 4.3 (a, b,) further
shows the effect of scale on point feature elimination.
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Figure: Simplification accompanied by scale
reduction
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Figure: Simplification applied to a constant scale
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Simplification manipulation
procedure• Simplification manipulation procedure is
applicable to points, areas and all other types of
features as illustrated in the accompanying
figures.• Depending on the scale of the map, the amount
of detail or convenience desired, some features
and very often those smaller than those desired
may be eliminated, e.g. small outliers as lakes,bridges, streams as shown in Figures 4.4, 4.5,
and 4.6.
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Confusion?
• To many map users, this procedure may
introduce a source of confusion in map
information but this is for the convenience
of both the map maker and user alike.
• The procedure could equally be applied to
areas by specifying minimum area or sizeor distance to be eliminated or retained.
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SCALE LAKES
STREAM NETWORK
LARGE SCALE
MAP
SMALL SCALE
MAP
Figure: Feature elimination, (Lakes & streams).
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Smoothing routines
• Instead of eliminating features, cartographers cansimplify a map by smoothing features.
• As is quite evident with linear features, their form may
further be simplified by removing detail from the edgesas illustrated in Figure 4.7
• In digital mapping smoothing may be carried out by use
of smoothing operators and surface models such as
moving averages and contrast stretching.
• Other routines for carrying out simplification include
measurement level reduction.
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SCALE COASTLINE WOOD
LARGESCALE MAP
SMALL
SCALE MAP
Map simplification through line smoothing
(Coastline & Woods/Forest)
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SYMBOLIZATION METHODS
• Have you ever noticed that some maps are
easier to understand than others? Often the
difference is due to the mapmaker’s choice and
arrangement of symbols and text.
• A map is most effective when its symbols are
easy to distinguish and their meaning is intuitive.
•
• Your choice of symbols and labels will be
influenced by the type of map you are making.
S b li ti
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Symbolization
cartographers’ vocabulary• Symbolization, along with selection, classification and
simplification make up the cartographic generalization
process. Symbolization is the graphic coding of the
selected and grouped essential characteristics,
comparative significances and relative positions(Robinson, et al 1978).
• It is the cartographers’ vocabulary; hence it is the
map’s language. As you have seen in Unit 2, the map
user must be able to communicate with thecartographer to get the required information.
Therefore the choice, designing and positioning of
symbols is very important to make the map serve its
purpose.
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Meaning and purpose of symbols
• The issue of symbols and their meaning is therefore particularly
crucial in cartography. Since symbols give meaning to the map, it
must be the case then that they have to be carefully chosen,designed and located or represented in order to convey to the map
user adequate and accurate information regarding earth reality.
• The process of creating graphic symbols to represent feature
attribute values of reality is what we call symbolization (Robinsonet. al). The cartographer turns to the symbolization process after he
had applied classification, simplification/exaggeration routines to
features selected for mapping.
• We can therefore refer to symbolization as the use of visual
variables to represent the summarizations resulting from
classification, and simplification/exaggeration. This is the
graphic coding or application of symbols that makes generalization
possible.
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IMPORTANT REMINDER
While you can conclude that symbolization is critical to the
success of any map, you must also realize the following: _________________________________________
Good simplification and classification
procedures can be nullified by poor
symbolization
Good symbolization can enhance the
effectiveness of simplification and
classificationGood symbolization can also impart/give an
unwarranted impression of accuracy to poorly
simplified or classified data.
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The symbolization problem
• In order to ensure good symbolization,cartographers usually perform two important
tasks before they choose their symbols.
• They must:
• Select ( and possibly change) the
measurement level of the original data
values, and
• Conceptualize the dimension for each
feature they wish to portray
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Types of graphic symbols
Cartographic symbols are either graphic orphotographic (colour, hue, grey tones of black
and white). Graphic symbols are commonly
grouped in three main categories according totheir shape:
• Pictorial or descriptive symbols• Geometrical or abstract symbols
• Letter or number symbols
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Measurement scale level
• Most symbols connote only qualitative(nominal) or quantitative (ordinal, interval,
or ratio) data.
• While in measurement theory thedistinction between interval and ratio data
is important, this distinction makes little or
no difference in symbolizing features.
• The only way we can portray interval or
ratio scales is to use textual or numerical
annotations to enhance the symbols.
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Examples of differentiation of point, line and area feature on a
nominal scale measurement.
POINT LINE AREA
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TYPE Qualitative Distinction
Quantitative Distinction
Point Symbols
Line Symbols
Area Symbols
Volume Symbols
R i Q ti
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Review Questions
• The map is necessarily selective. Discussthis statement with reference to any
relevant cartographic generalization
process
• Identify and discuss briefly the principal
cartographic generalization processes youwould employ for a major mapping project
in Ghana
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