Geographic Information Systems : toward a Geo - Relational Structure

The paper distinguishes features of computer-aided mapping and geographic information systems and identifies an emerging link. Common to both systems is the need to link graphic data and attribute data. This geo-relational structure requires a one-to-one relationship of the graphic record with the record of the table of attributes. Combining distance-referenced line data with a topological data structure is the key to a powerful geographical information system. INFORMATION The similarities and differences between a system for computer-aided mapping (CAM) and a geographic information system (CIS) are difficult to articulate, but important. The following definitions are offered as a means of initiating this presentation of distinguishing features: 1. A CIS is defined as a specialized information system in which locational identifiers are attached to data for spatial analysis and/or mapping. Thus a CIS provides spatial information to users for decision making in management, planning, and research. Importantly a CIS allows the spatial collation of separately collected data. Cartographic modeling or overlaying is employed for analysis across layers of data to express the spatial relationship among the variables. 2. On the other hand, computer-aided mapping is a more limited display of layers of data with the ability to select layers, window, scale, and display, but without the ability for analysis across layers. These definitions ignore a feature that both kinds of systems are stretching to meet — a data base management system that relates objects on the map to records in data files containing attributes of those map objects. This portends that the distinctions identified in the definitions will diminish. This will be illustrated by the subsequent development of a geo-relational structured CIS. The purpose of the paper is to distinguish better between computer-aided mapping and a CIS and to identify an emerging link. Although the distinctions are becoming less in actuality as systems evolve and mature, it is important to understand and to be able to describe clearly the difference. Belaboring the distinctions draws attention to the required properties and power of the CIS, while exploring ways by which •'•Not to be confused with Computer-Aided Manufacturing (CAM) systems.