Author:
Rufino Pérez Gómez
Professor of Digital Cartography
University School of Topographic, Technical Engineering
Universidad Politécnica de Madrid

Abstract

Map production has often been a slow and costly task. The development of computer technologies such as Geographic Information Systems and Digital Terrain Modelling have increased a lot the possibilities for analysis and representation of geographical phenomena. This paper explores the integration of cartographic and mathematical concepts, together with computer tools.

1.- INTRODUCTION

Map production has historically been a slow and costly task. At the end of the XIXth century and at the beginning of the XXth, there was a sudden interest in the graphic description of the surface of the earth. This resulted in a great development of Thematic Cartography. However, this type of "inventory map" was only static photos of dynamic phenomena. It would therefore be a limiting factor to Cartography when dealing with any geo-referential phenomenon.

The mathematical developments that took place as from the thirties, together with the introduction of Geographic Information Systems in the sixties, have greatly and positively impacted the modelling and analysis of any geographical phenomenon. Besides, Remote Sensing Techniques make use of an increasing number of satellites whose spectral and spatial resolutions are subject to constant enhancement. The Landsat 7, launched in April 1999, and high resolution satellites capable of covering small areas with a 1 metre resolution, are good examples of the potentialities this data capturing technique has. Finally, Global Positioning Systems (GPS) and Digital Photogrammetry techniques play an important role in the updating of the existing cartography, or in the formation of digital cartographic databases.

Cartographic Techniques provide for the synoptic and abbreviated representation of the great many data captured and processed when modelling a environment concern. However, Multimedia Techniques can complete and increase our capacity to transmit Geographic information under three-dimensional animated representations. Finally, the rapid advance of Internet allows disseminating the results of each project to a great number of users.

Within the wide range of the Sciences and Technologies mentioned, this congress will focus its attention on two concrete aspects: the production of thematic cartography from Geographic Information Systems (GIS) and the production of cartography from Digital Terrain Models (DTM). Final Projects written by our students will, in both cases, conduct the debate. These projects are required to be granted the Degree of Technical Engineer in Topography.

2.- PRODUCTION OF THEMATIC CARTOGRAPHY FROM A GEOGRAPHIC INFORMATION SYSTEM.

In traditional Cartographic Techniques, map production has its own workflow. However, Geographic Information Systems structure a flexible data access through consultation and analysis modules. A thematic map represents the visualisation of the answer to a question in the context of a Geographic problem. GIS capabilities allow a lot of questions and the resulting and varied Thematic Cartography is profitable. This profitability can express the spatial distribution of a socio-economic variable, or can represent a subset of regions that meet a multi criterion of factors of positive localisation. Anyway, the final maps will meet the theoretical principles of Graphic Semiology by the effective application of perceptive perspectives of visual variables.

The following project has been developed to illustrate the methodology explained in the previous paragraph. We have collected, from the National Institute of Statistics (Instituto Nacional de Estadística_INE) website, data corresponding to 179 districts located in the Community of Madrid. These data refer to tourism, health, social services and other socio-economic variables.

The Internet alphanumeric data were digitalised, loaded into a Database and then logged onto the maps of the project area while building up the Geographic Information System. A key element is to identify the variables required by a greater number of users and structure them as fields of graphic tables. The rest of the variables, a large number probably, will be structured in different non-graphic tables. Graphic tables have an interface to connect them to non-graphic tables through the INE code relative to each district selected as "join field”.

As many multi-table views as required are created during the analysis. The consulting object will always be a Geographic entity linked to a graphic table or a Geographic entity linked to a multi-table view. Once the described structure has been created, the topological analysis modules can quickly and easily produce multiple quantitative or qualitative maps.

3.- PRODUCTION OF THEMATIC CARTOGRAPHY FROM DIGITAL TERRAIN MODELS.

Terrain topography greatly influences numerous variables that participate in the dynamics of ecosystems. Height, slope and slope orientation are key variables to the understanding of many Geographic phenomena.

At present, the Surveying engineer can resort to Digital Terrain Models to model the surface of the earth mathematically. These geo-referenced and three-dimensional models are a key element to the analysis of engineering, environmental and territorial planning projects.

It is worth mentioning among the multiple applications of Digital Models, manipulations, analysis and representations for cartography. We will highlight maps with level curves, high resolution shaded reliefs, slope maps, orientation maps, overlaying of raster orthoimages, perspective views, three-dimensional animations with diversity of materials.

The success of this type of technologies depends on the adequate integration of cartographic and mathematical concepts with computer tools (CAD 3D, GIS and DTM, Digital Treatment of Images). Therefore, teaching must rest on a detailed understanding of concepts and not on the use of open complex programs with multiple options.

By contrast, different concepts and tools can be used jointly to get novel products that will enrich our possibilities of analysis and interpretation. For example, a digital orthoimage can be geo-referenced and highlighted radiometrically and then superimposed over a digital model in the project's area. Later on, it will be possible to generate a perspective, comprehensive view and resort to the multiple photographic possibilities provided by CAD. Alternatively, three-dimensional symbols and materials could be superimposed over the digital model (street-lamps, benches, trees, etc.) to generate animated sequences of the scene with a good level of realism.

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