IDECAP is an interactive system for displaying maps of the Dutch 1971 census and 1978 land use data. The system is implemented on a PDP-11/45 in augmented C, and on a VAX11/780 in augmented PASCAL. In each case the augmentation is “input/output tools,” which are “interaction modules” implementing rules for the system’s response to user stimuli. The displays show values taken from a small (:9I10 Mbytes) database that has been preprocessed into 500m:9I500m cells, overlaid on a topographic/cadastral outline base, resembling grid cell social atlases such as [1]. Through menus, the user can select the region to be displayed, map scale, variables(s), class intervals, symbols, and colors. With a color monitor two variables can be shown simultaneously, one represented by the size and the other by the color of the symbol. The authors cite seven (not very recent) similar systems and discuss possible extensions, but they suggest possible enhancement difficulties resulting from the hierarchical database structure. The original data and the grid cell transformation are not discussed.

The paper stresses the graphics and user interface, which are described by example rather than formally. The point of departure is that analog displays (such as maps) allow the viewer to use his or her pattern-recognition faculties; this also limits the system development problem to obtaining user requests and displaying data. IDECAP is a display system, and the human does the interpretation -- this is a reasonable division of labor, although not a geographic information system.