1Wiener Schriften zur Geographie und Kartographie, Band 17, Wien 2006, S. …-…

CAJTHAML, Jiri (Prague)*

Publishing Old Maps via the Internet: An Overview of Possibilities

Content

Summary ..........................................................................................................................................................Zusammenfassung ...........................................................................................................................................1 Introduction ................................................................................................................................................2 Vector Drawing vs. Raster ...........................................................................................................................3 Digital Data Publishing ................................................................................................................................4 Possibilities for Internet Map Publishing .....................................................................................................5 How Can the Internet Application Look Like? .............................................................................................6 Hardware and Software Selection ..............................................................................................................7 An Example of a Simple Application for Old Maps Presentation via the Internet .........................................8 Conclusion .................................................................................................................................................9 References .................................................................................................................................................10 List of Figures .............................................................................................................................................

Summary

Cartography is a science with a wealthy history. In fact, the first drawings of mammoth hunters were the first maps believed to have been produced. With the arrival of digital technologies, almost every branch of science has changed, including cartography. Computer technologies, which were initially used only for cartographic re-search, have now taken over cartographic production. After establishing digital cartography as the main method for practical production in the 1990s, the Internet provides an ideal medium for map delivery and presentation. Contemporary technology allows more than just map browsing. Cartographic data can be shared using dif-ferent servers and users can work with data interactively in an Internet environment. This paper addresses the contemporary possibilities of publishing map data on the Internet.

Zusammenfassung

Kartographie ist eine Wissenschaft mit reicher Geschichte. Schon die ersten Malereien der Mammutjäger waren eigentlich Vorgänger der heutigen Karten. Mit dem Einzug der digitalen Technologien ändern sich allmählich alle wissenschaftlichen Fachrichtungen, wie auch die Kartographie. Computertechnologien, die zu Beginn in der Kartographie mehr zur Forschung dienten, haben heute praktisch die gesamte kartographische Bildung beherrscht. Nachdem in der Hälfte der neunziger Jahre des vergangenen Jahrhunderts in die Praxis digitale Methoden der Kartenbildung standardmäßig eingeführt wurden, kommt mit dem neuen Jahrhundert der Inter-netdienst als ein ideales Medium zur Präsentation dieser Daten. Derzeitige technologische Möglichkeiten bieten mehr als bloße Kartendarstellung an. Kartographische Daten können an verschiedenen Servern geteilt werden und mit den Daten kann man interaktiv direkt im Internet arbeiten. Eben mit solchen derzeitigen Möglichkeiten der Datenpublikation im Internet beschäftigt sich dieser Beitrag.

* Ing. Jiri CAJTHAML, Department of Mapping and Cartography, Faculty of Civil Engineering, Czech Technical University in Prague, CZ-166 29 Prague, Thakurova 7, Czech Republic

1 Introduction

Maps are almost entirely made by computers nowa-days, and map drawing is generally created as a vec-tor file. With the existing paper maps, they have to be scanned, producing a raster file. As there exists many possibilities for map production this paper covers the

basic groups of software useable for producing car-tography: vector drawing programs (Adobe Illustrator, Corel DRAW, Macromedia FreeHand), CAD systems (Autodesk AutoCAD, Bentley MicroStation), special-ized cartographic products (OCAD), geographic infor-mation systems (ESRI ArcGIS, Intergraph GeoMedia, MapInfo). Every group has specific advantages and

2 CAJTHAML, J.: Publishing Old Maps via the Internet: An Overview of Possibilities

disadvantages. However, when scanning old paper maps only raster data format is possible.

Maps can be published in two fundamental forms: analog; or digital. Printed (analog) maps are mostly created from vector data. For final adjustments various DTP applications are used. Finally, data is converted into print formats like PDF or PostScript and then transferred for printing. Digital data can be published in various desktop application formats or via the In-ternet. Practically every software product works with its own vector or raster file format. Therefore, data publishing should be done in an open data format (instead of using one of the many proprietary formats available). The Internet also needs standard formats for data publishing. If data is to be published using the Internet, the data must often be converted. For vector graphics, there are the SVG and GML formats and for raster images there are JPEG and PNG formats suit-able for Internet publishing.

Old map publishing always works with raster images. Maps must be scanned at high resolution and then modified for later publishing. If only static images are required for simple HTML publishing, raster data should only be converted into JPEG or PNG images and placed onto the server for user access. If more interactivity is needed (zoom, pan), then some other application must be used. This type of application is mostly based on XHTML. In this case the application can only work with the raw image, without georef-erencing (e.g. Zoomify). To work with images with a coordinate system, powerful application map server applications are required (UMN MapServer, ArcIMS, Geomedia WebMap, MapXtreme and MapGuide). Map servers also enable other data layers to be con-nected (either as vector or raster images), and also data shared by other servers (within the frame of Web Map Services). With this functionality, simple GIS tools can be provided using the Internet.

In the sample application that is described in the paper, scanned maps from the 2nd Military Mapping Survey of Austria-Hungary covering the area of Czech Republic (1836-1852) were used. Data was georefer-enced and made available using the Internet with the contemporary coordinate system S-JTSK (published by UMN MapServer). Data from these maps can then be compared with the present state of the landscape by linking other map layers (orthophoto maps, vector drawings, etc.) to the scanned maps.

2 Vector Drawing vs. Raster

When we look at digital graphic data, we can divide them into two main groups: vector and raster images. Vector drawings are represented by geometric ele-ments (points, lines, and polygons). Raster data is represented by pixel values (picture elements). This basic definition shows that vector drawings are better

for the map production. Basically, these maps consist of points, lines, and polygons. Raster data mostly serves as a basic layer for later vector creation. Or-thophoto maps, satellite images, and even scanned paper maps can be used in this way.

2.1 Vector Data

There are many programs for vector drawing creation. Each of them has their specific functions. They can be divided into four basic groups:• vector graphic systems• CAD systems• specialized cartographic software• GIS (Geographic Information Systems)

Vector graphic programs are not primarily designed for map-making. They can work with drawings, es-pecially in the field of professional printing or DTP. Their main advantages are their advanced graphic functions – pre-press support functions, high-qual-ity printing format export and their relative low cost (under US$500 per license). A negative aspect is the impossibility of working in things like cartographic projections and the number of functions that are use-less for cartography. As well, specialized functions are non-existent. In this category are Adobe Illustrator, Corel DRAW, and Macromedia FreeHand. Avenza MAPublisher sits between a vector graphic system and a GIS (superstructures of Illustrator or FreeHand). Vector graphic programs are suitable for quality map output, if they are not too complicated (plans, over-view maps, etc.). These products are usually used as an intermediate step (mostly pre-press) between cartographic work and printing.

CAD (Computer-Aided Drawing systems) are intended for technical drawing creation. Nevertheless, they are used in cartographic production. They provide quality artwork using vectors, but their support for raster im-ages is not ideal. Their high cost is the main disadvan-tage of these packages. In this category are Autodesk AutoCAD and Bentley MicroStation. An alternative product, Autodesk Map3D lies between CAD and GIS. CAD systems are used mostly for technical drawings, eventually technical maps. They are used for cadastral data management in the Czech Republic.

Products which belong to the group of specialized cartographic software combine characteristics of all other software solutions. Simplicity, speed of work and high-quality output is desirable in cartography. Everything should be done for minimal cost. OCAD is representative of this group, a product designed for orienteering map-making, but widely used for tourist maps or city plans production. The software is rela-tively simple to use and allows users to work quickly. Despite these advantages, it is only a drawing tool with some specific cartographic functions.

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GIS (Geographic Information Systems) are seen to be the most advanced cartographic production tools. GIS is ideal for geographical data management. Vec-tor data is stored together with associated attribute tables, ideally in one spatial database. GIS offers advanced tools (topology verification, disconnected editing, versioning, etc.). Unfortunately, GIS software is relatively expensive and their cartographic output is not seen as ideal. Despite their high costs, GIS is seen to be the right solution for cartographic production. GIS software includes not only tools for cartographic output, but also many functions for data arrangement, efficient data management and later use. They can be used in conjunction with DTP software for output. In this category are ESRI ArcGIS, Intergraph GeoMedia and MapInfo.

Practically every one of these solutions manages its own vector data format. Some of them are partially open, but an ideal format for data transfer using a sin-gle system did not exist for a long time. With the avail-ability of XML work on a standard spatial data format began. GML (Geography Markup Language) format was established. It is able to store vector drawings along with their attribute tables. GML transfer is seen to be the best solution for GIS data exchange. With the widespread use of the Internet it was necessary to create a uniform format for vector drawing displays on the Internet. SVG (Scalable Vector Graphics) was created for this application.

2.2 Raster Data

In the area of raster data, the situation is not so com-plicated as with vector data. Raster consists of picture elements (pixels). As the original formats of raster im-ages were various, there are now only a few widely-used raster data formats. Raster data can be stored either raw or compressed. This is necessary because of large amount of raw raster data available. The most widely-used formats are TIFF (raw or with different compression – LZW, PackBits), JPEG (compressed), BMP, GIF, PNG, ECW. Raster images can also carry information about their spatial position (they can be georeferenced). This information can be placed right in the file header (GeoTIFF) or in an external file (ESRI world file – TFW, JGW). Referenced raster then con-sists of two files (TIFF-TFW, JPEG-JGW).

The best formats for Internet publication are JPEG (lossy compression), PNG (lossless compression) and TIFF (lossless LZW compression). A very effec-tive compression algorithm is offered by the MrSID format, which is unfortunately not an open format. When working with raster data, the purpose that the raster image will be used for needs to be established and an appropriate compression method and data format chosen.

3 Digital Data Publishing

Digital data created using cartographic software pack-ages (original vector, rasterized vector, or scanned map) can be published in different ways. Data may be distributed as files on CD-ROM, DVD, or via FTP or HTTP servers. In this case the user must have a desktop application which can read these data files. There are no problems with raster data, because many free raster viewers are available. Despite this, the amount of data is large and data download rates are therefore slow. Vector data are usually rasterized before publishing, and so users cannot edit the data or change the symbology. Here, data is only provided for browsing. If we are concerned about publishing data for editing, we will probably choose CD-ROM or DVD for data distribution, allowing users to open data files using their own application. If we are concerned about only viewing data, then the Internet is an ideal medium.

4 Possibilities for Internet Map Publishing

The following sections cover the possibilities for plac-ing maps onto the Internet.

4.1 Raster presentation

This possibility presents only a raster image (either scanned maps or maps directly computer-created). Images are presented as part of a XHTML page and tools to work with the map are not required. The map provides only a static image. The whole image can also be used as a button to redirect user to another Web page. On the main page, small images are generally provided which work as buttons. Every button links to the map displayed at a higher resolution. HTML has an enhanced application called “clickable maps”. The main image can be divided into many regions and every region can behave as a single button. With this improvement, the main image can be used as a reference page, providing an overview that consists of the map sheet limits. Clicking into any region on this overview map will re-direct the user to the page providing a full-resolution map sheet.

4.2 Static web mapping

Static web mapping is based on sending variables by a XHTML form to a CGI application that resides on a server. The main XHTML page contains the XHTML form with many buttons and checkboxes. Through the HTTP protocol, the form can send variables to a CGI application stored on the server. This application extracts values of variables and returns this informa-tion to the XHTML page image of the map generated

4 CAJTHAML, J.: Publishing Old Maps via the Internet: An Overview of Possibilities

from data storage. CGI applications are usually called “mapservers”.

4.3 Interactive web mapping

Interactive web mapping increases the functionality of static web mapping through the use of some inter-active technologies (DHTML, Java applets, ActiveX, etc.). DHTML technology is based on user-side script-ing (JavaScript, VB Script), DOM (document object model) and CSS (cascading style sheets). Then, us-ing simple scripts, users can work more interactively. Another possibility is to use some Internet browser plug-ins (Java support, Flash, etc.).

4.4 Web Map Services

Web Map Services are a perfect way to share data via the Internet. In client-server applications, data is stored on the server and the client does not need any data to reside on their computer. Web Map Services enable data sharing between servers. Data is not needed on the server, data can be linked from another server. If the map server keeps to OGC specifica-tions, there is no problem to share data. The two most common services are WMS (Web Map Service) and WFS (Web Feature Services). WMS allows raster data sharing (transfer in JPEG, TIFF, and PNG), WFS allows vector data sharing. However, much vector data is still shared as raster images by WMS. To share real vector data, WFS must be used, where data is transferred in GML format. Every server application can then work as WMS/WFS server or client.

5 How Can the Internet Application Look Like?

Advanced GIS Internet application could consist of: • client (with optional plug-ins),• web server,• map server,• data server.

How does the information transfer work? The client sends a request to an URL address. This request is then sent to the Web server using the HTTP proto-col. The Web server analyzes this request, finds the method of parameter sending (GET or POST) and connects to the CGI application (mapserver) with the appropriate parameters. The map server reconstructs the form data and collects appropriate data from the data server. Then the mapserver creates images (map, scale bar, reference map) and sends them back to the Web server. The Web server combines images with the rest of the XHTML page and sends the whole page to the client. The page is sent using the HTTP protocol. Finally, the client displays the page client-side.

6 Hardware and Software Selection

During Internet application development, it is neces-sary to specify the correct hardware and software. It is always necessary to think about both sides of the application – server and client.

6.1 Hardware

The server is the central unit of the application. It should be equipped with high-quality processor and sufficient memory (RAM). Hard disks with sufficient space are used for data storage. All single server ele-ments (Web server, map server and data server) can be run on one computer for simpler applications. For larger projects, it is, however, preferable to run every part on independent computer. The client section of the application can be run on a standard PC. On the both sides of the application, Internet connectivity is very important. It determines the speed of the whole application.

6.2 Software

Every server or client must be run under an operating system (OS). Microsoft Windows is the most wide-spread OS in use, but Linux is being used more and more, especially in servers. Apache is the most-used Web server. It is a high-quality product that is free. In the field of map servers, there are many usable prod-ucts. We can choose commercial products (ESRI Ar-cIMS, GeoMedia WebMap, MapInfo MapXtreme, Au-todesk MapGuide) or free products (UMN MapServer, Deegree, geoserver). UMN MapServer is very suitable and it is probably the most widely used application. If data is stored in a database it is necessary to choose an appropriate database system. Again, the choice is between commercial products (Oracle, MS SQL) and free products (PostgreSQL, MySQL and Firebird). For spatial data storage there are spatial superstructures of database systems (Oracle Spatial, PostGIS, etc.).

7 An Example of a Simple Application for Old Maps Presentation via the Internet

Within the frame of doctoral studies, the author has created simple applications for old map presenta-tion using the Internet. The application was run on a standard PC with the Windows XP operating system. The software configuration consisted of Web server Apache 2.0.54 with the UMN MapServer 4.4.0. A database was not used (data are stored in the file system).

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7.1 Application data

The data is the heart of the application. The main da-taset consisted of raster images from the 2nd Military Mapping Survey of Austria-Hungary. These maps were created in the 19th century and the coordinate system of the maps is based on then cadastral survey. If a seamless map is required, every map sheet must be prepared. The following steps must be completed for every map sheet: • crop the image behind the map frame;• set the image transparency; • save the image as a TIFF with LZW compression;• georeference the image (transform to corner coor-

dinates); and• save the image world file (TFW).

Once the georeferenced raster images are available they can be added to the map file (UMN MapServer project configuration file). Unfortunately, there is one problem. Raster images should be displayed as fast as possible. For publishing a large raster dataset, another technique needs to be used – tile indexing. The shapefile with polygons as borders of every map sheet is created and added to the map file. Every poly-gon in this shape file refers to specific raster image. During display MapServer checks the shapefile and displays only the needed raster images. Tile index can be easily created by the script “gdaltindex”, which is the part of MapServer bundle installation (GDAL li-brary). Another problem of display is the need to load a large amount of data, even when displaying raster data at a small scale. For reduction pyramid building

Fig. 1: Screenshots from the mapserver application

6 CAJTHAML, J.: Publishing Old Maps via the Internet: An Overview of Possibilities

is required. Raster images can be projected over a few levels with different pixel size. For example, if an original raster has a 1-meter pixel resolution, pyramid levels for pixel size 2 meters, 4 meters, 8 meters, and 16 meters, etc. can be built. Pyramids are still stored in the original file (TIFF). During display, MapServer checks the scale and uses only the needed level of the pyramid. Pyramids can be easily created by the script “gdaladdo” which is also the part of MapServer bundle installation (GDAL library).

7.2 Creation of the application

The created application represents a simple form of interactive Web mapping. It is based on the CGI pro-gram UMN MapServer, which communicates with the Web server. The Internet page contains a XHTML form. Using the “GET” method, values of variables are sent from the form. The Web server forwards these values to the UMN MapServer. It reacts and sends back appropriate images. Finally, the whole Internet page is sent back to the client. Because XHTML forms enable only static application creation, this needed an improvement. Several functions were programmed in JavaScript for interactive coordinate reading during mouse movement. Then functions were programmed for buttons for moving the map in eight basic direc-tions. With the help of Java applet jBox, a dynamic rectangle zoom was enabled. Demonstrations of the application are provided on a separated page.

7.3 How the Application Can Be Used

As well as data from the 2nd Military Mapping Survey of Austria-Hungary, some other data layers were added to the application. Some data using WMS were also connected. Old maps can be then very simply com-pared with the contemporary state of the landscape. This type of data is especially valuable for landscape engineers and environmental applications. The best way to make this data accessible is WMS distribu-tion. This implementation is currently being worked-upon.

8 Conclusion

In this paper, one of the possibilities of geographic data publishing using the Internet was introduced. Creating such an application is relatively simple and the creator need not be a programmer. Publishing old maps can be used in many ways, not just for viewing, but also for environmental research. Web map servers are more and more common on the Internet. If WMS and WFS are widely used, the future of cartography will be promising.

This research has been supported by GA CR grant No. GA 205/04/0888 – Georeferencing and the Car-tographical Analysis of the Historical Maps of Czechia, Moravia and Silesia

9 References

CAJTHAML J. (2006), Mapserver of the old maps. In: GIS Ostrava 2006 (conf. paper).

ČADA V. (2005), Geodetické základy státních mapových děl 1. poloviny 19. století a lokalizace do S-JTSK. In: Historické mapy, Kartografická spoločnosť Sloven-skej republiky, Bratislava (conf. paper).

OPEN GEOSPATIAL CONSORTIUM (2004), OpenGIS Geography Markup Language (GML) Encoding Specification. Retrieved 2005-06-21 from http://www.opengeo-spatial.org/specs/?page=specs

OPEN GEOSPATIAL CONSORTIUM (2005), OpenGIS Web Service Common Implementation Specification. Retrieved 2005-06-26 from http://www.opengeospatial.org/specs/?page=specs

W3C CONSORTIUM (2003), Scalable Vector Graphics 1.1 Spec-ification. Retrieved 2005-06-28 from http://www.w3.org/TR/SVG/

UMN MapServer homepage (2005) Retrieved 2005-06-11 from http://mapserver.gis.umn.edu/

10 List of Figures

Fig. 1: Screenshots from the mapserver applica-tion