Geographic Information Systems: An Introduction, 3rd Edition

16.5 Final Comments

Beautiful final products may, of course, hide poor-quality data. Data uncertainty is not easily shown in graphic form. Most experience of showing data uncertainty relates to geometric accuracy, less to showing attribute accuracy, maintenance status, completeness, and logical consistency. Uncertain boundaries between polygons can be shown by dashed lines, double lines, a line darker in its middle and lighter toward its edges, or as a zone of a particular color or of no color at all. Uncertain points can be indicated by circles of differing size and color or as vectors. The network, deformed in proportion to the uncertainty in the point basis, is also one way of showing data quality. A digital terrain model (DTM) can be used with very good effect by placing the size of the uncertainty on the z axis. It is also possible to decide to use a more powerful generalization for inaccurate data than for exact data. Attempts have been made to use blinking lights or sound signals to indicate uncertainty. Today there is no available GIS system that can automatically handle visualization of the quality of data in a satisfactory manner.

Maps are static presentations that are not particularly suited to showing temporal changes. But animation techniques can bring on-screen maps to life. For example, maps may be displayed in rapid sequence to illustrate a particular trend, such as the day-by-day spread of radioactive fallout from Chernobyl during the first two weeks following ...