A system for interactive acquisition and administration of geometric data for thematic map production

Abstract

Most computer assisted information systems for planning purposes are designed to produce thematic maps as output. Graphic data processing, on the other hand, has not yet reached the degree of perfection already achieved in other fields of EDP, e.g. commercial and statistical applications. The author and his collegues are integrating cartographic data and presentation techniques gradually into an information system.Within the system being described, the geometric data base is considered as a line network. The edges of the network are represented by strings of orthogonal coordinates (Segment definitions). A unique identifier is assigned to each coordinate string, and the areal units are defined by a sequence of edge identifiers (Polygon definitions).In order to obtain error-free files, strict rules have to be observed and a high degree of accuracy has to be achieved.For this purpose, an interactive system - DIGNET - has been developed to fullfill these objectives: (1) guide the operator through the digitizing session, (2) ask for the appropriate input, (3) create the reference tables, (4) react to erroneous input and operation, (5) detect digitizer malfunctions, (6) allow immediate graphic replay of the digitized data.In order to facilitate the manipulation of the boundary network files, a number of utility programs have been added to the DIGNET-System; among them (1) DIGEDI - to prepare maps for digitzing, (2) DIGLIST - to list all results from digitizing sessions, (3) DIGMERGE - to merge two or more submaps into one final map.

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