Geographic Information Systems: An Introduction, 3rd Edition

15.4 GIS Analytic Models

Several theoretical models have been evolved to exploit GIS analytic functions. The three prime examples are cartographic algebra, expert systems, and linear combinations. The models must be regarded as aids to expert judgment, because the drawback in all of them is that they are based on theoretical assumptions that cannot cover all practical situations.

15.4.1 Cartographic algebra

Cartographic algebra is based on the assumption that a set of simple operations can be found and joined sequentially to constitute relatively complex modeling (Figure 15.13). This process starts with an existing set of attribute tables, which are then processed in a sequence of operations, each of which produces a new column in a table. Finally, the attribute sought is compiled. It may be represented by a flowchart in which the thematic map is processed successively until the final version is produced (Strand 1991a).

Figure 15.13

Cartographic algebra. Thematic layers A, B, and C with their own attribute tables (a) are manipulated by simple operations (b) to a new thematic layer and attribute tables (c), which are, again, by a simple operation, manipulated to one result layer (d) and a result attribute table (e).

Cartographic algebra may require the following operations:

• Reclassification
• Averaging
• Maximizing
• Subtracting
• Adding
• Scattering
• Streaming

The success of the model is ...