A Feature-Based Geographic Information System Model

A conceptual model for structuring features in a geographic information system (GIS) is presented. The model includes spatial, thematic, and temporal dimensions and structures attributes and relationships for each dimension to build a feature-based GIs. The model is grounded in an entity-based view of geographic phenomena and requires representation of geographic entities as feature objects in GIS. The model is built on concepts from region theory in geography, category theory in cognitive psychology, and dafa modeling theories, including abstraction and generalization concepts in cartography and G I ~ . The feature construct provides direct access to spatial, thematic, and temporal attributes and relationships and thus supports multiple representations and multiple geometries, such as raster and vector. The rich structure has potential application for spatial analysis and sophisticated geographic process models. Resolution and application dependencies of feature-based systems are discussed with tools to aid in feature determination. Example features are included with parts of the model explicated for these examples. Introduction The development of geographic information systems (GIs) has advanced to the point that alternative approaches for modeling geographic phenomena can now be implemented. The conventional map framework based on layers of geography appears inadequate to handle sophisticated geographic process models and spatial analysis approaches (Goodchild, 1987; Goodchild, 1991; Nyerges, 1991). Few would argue the need to develop better interfaces to GIS in which users are able to name geographic entities and perform analyses on those named entities. The difficulty occurs in whether the underlying data model need reflect these entities directly or whether, through sophisticated data processing, these entities can be presented to the user through conventional layerbased models. This paper is developed from the assumption that the user's perception of geographic reality is one of geographic entities such as roads, buildings, hills, and ethnic immigration areas rather than one of layers of data, and that it is desirable for the data model to directly reflect this perception. Given this assumption, the design for an objectbased model in which objects are a direct representation of the geographic features rather than of geometric elements such as point, line, and area is developed. This design is referred to as a feature-based geographic information system (FBGIS) because the term "feature" encompasses both the geographical entity and its object representation (NCDCDS, 1988). In order to model geographic phenomena from reality, some subset of that reality, i.e., an idea of geographic reality, must be developed which reflects a particular application Department of Geography, The University of Georgia, Room 204, GGS Building, Athens, GA 30602-2502. PE&RS July 1996 TABLE I. DIMENSIONS, A ~ R I B U T E S , AND RELATIONSHIPS OF THE FBGlS CONCEPTUAL MODEL