Introducing Geographic Information Systems with ArcGIS: A Workbook Approach to Learning GIS, 3rd Edition

Moving Spatial Data from Maps to Computers: Forces for Change

Force for Change #1: There Are Difficulties and Limitations with Using Maps for Decision Making

Maps can depict things beautifully and usefully, so for many applications, a paper map is exactly what is needed. But for many purposes maps are hard to use, for these reasons:

• A map is a compromise between a storage function and a display function. As more and more information is stored on a map, it becomes more cluttered. At some point, it becomes unreadable. A map that stored every theme of interest to everyone would be black. Aeronautical charts are a good example of this problem. The aeronautical charts of the 1950s were pretty simple affairs, showing terrain, prominent features, and some airport information. As new regulations came into effect, and new communication facilities were established (whose radio frequencies were placed on the map), as new types of official airspaces were defined, as new military training grounds were introduced, the map had to depict more and more. As a consequence, without careful study (not an activity that can easily take place in the cockpit of an airplane, where the primary activity should be piloting), it is easy to misread such a cluttered map. In a GIS, the storage function and the display function are separated. When display is required, a map can be constructed of only those themes wanted by the user.
• It is difficult to analyze a map. Consider a map that shows highways. Suppose ...