Visualization

One of the main goals of the GIS is to present spatial information in an efficient way. In this context the cartographic visualization process is considered to be the translation or conversion of spatial data from a database into graphics. During the visualization process, cartographic methods and techniques are applied. These can be considered to form a kind of "Cartographic Grammar", that allows for the optimal design, production, and use of maps.

The visualization process is guided by the question “How do I say what to whom?” “How” refers to cartographic methods and techniques; “I” represents the cartographer or map-maker; “say” deals with communicating in graphics the semantics of the spatial data; “What” refers to the spatial data and its characteristics, (for instance, whether they are of a qualitative or quantitative nature); “Whom” refers to the map audience and the purpose of the map—a map for scientists requires a different approach than a map on the same topic aimed at children. 

The visualization process is always influenced by several factors, i.e. the answers to questions:

• Map scale -What will be the scale of the map: large, small, other?This introduces the problem of generalization. Generalization addresses the meaningful reduction of the map content during scale reduction.

• Map type - Are we dealing with topographic or thematic data? These two categories have traditionally resulted in different design approaches, as was explained in the previous subsection.

• Data Characteristics (measurement scale) - More important for the design is the question of whether the data to be represented are of a quantitative or qualitative nature.

Some of these questions can be answered by just looking at the content of the spatial database.

We should understand that the impact of these factors/answers may increase, since the compilation of maps by spatial data handling is often the result of combining different data sets of different quality and from different data sources, collected at different scales and stored in different map projections. Cartographers have all kind of tools available to visualize the data. These tools consist of functions, rules and habits. Algorithms used to classify the data or to smooth a polyline are examples of functions. Rules tell us, for instance, to use proportional symbols to display absolute quantities or to position an artificial light source in the northwest to create a shaded relief map. Habits or conventions—or traditions as some would call them—tell us to colour the sea blue, lowlands green and mountains brown. The efficiency of these tools depends partly on the above-mentioned factors and partly on what map users are used to.

The Role of the Cartographer

The producer of the visual products may be a professional cartographer, but they may also be an expert in a particular discipline, for instance someone mapping vegetation stands using remote sensing images or mapping health statistics in the slums of a city. To enable the translation from spatial data into graphics, we assume that the data are available and that the spatial database is well structured.

In the past, cartographers were often solely responsible for the whole map compilation process. During this process, incomplete and uncertain data often still resulted in an authoritative map. The maps created by a cartographer had to be accepted by the user: cartography, for a long time, was very much driven by supply rather than demand. In some respects, this is still the case. However, nowadays one accepts that just making maps is not the only purpose of cartography. The visualization process should also be tested for its effectiveness. To the proposition “How do I say what to whom” we have to add “and is it effective?” Based on feedback from map users, or knowledge about the effectiveness of cartographic solutions, we can decide whether improvements are needed, and derive recommendations for future application of those solutions. In particular, with all the visualization options available today, for example animated maps, multimedia and virtual reality, it is essential to test the effectiveness of cartographic methods and tools.

Some examples are the creation of a full, traditional topographic map sheet, a newspaper map, a sketch map, a map from an electronic atlas, an animation showing the growth of a city, a three-dimensional view of a building or a mountain, or even a real-time map display of traffic conditions. Other examples include “quick and dirty” views of part of the database, the map used during the updating process or during a spatial analysis. However, visualization can also be used for checking the consistency of the acquisition process or even the database structure. These visualization examples from different phases in the process of spatial data handling demonstrate the need for an integrated approach to geoinformatics. The environment in which the visualization process is executed can vary considerably. It can be done on a standalone, personal computer, a network computer linked to an intranet, or on the World WideWeb (WWW/Internet).