Geographic Information Systems: An Introduction, 3rd Edition

16.2 Graphic Generalization

We have previously discussed the need for generalization when the real world is transformed to GIS. In this connection we talked about generalization regarding content, or so-called conceptual generalization. In map presentation we use the term graphic generalization (Figure 16.5). The main function of graphic generalization is to ensure that important information on a map is registered more quickly than less important information. This is achieved by graphic effects such as simplification, adjustment, and smoothing. In concrete terms, this includes simplification of geometry, use of symbols, dividing data into groups (classification), and extension of the validity area of the data (extrapolation). The last two points, classification and extrapolation, are mainly related to statistical data. Moreover, the need for graphic generalization is closely linked to map scale, because small map scales require a greater degree of simplification, adjustment, and smoothing than larger map scales.

Typical examples of graphic generalization are the use of thick lines for important roads and thin lines for less important roads, and showing a settlement as a single area instead of using many small house symbols. Alternatively, areas that are located close to each other and represent the same type of object are joined together in one common surface. When thick lines are used for roads, the consequence can be that other objects (buildings, railroads, etc.) may have to ...