A UNIFIED SPATIAL MODEL FOR GIS

摘要

GIS (Geographic Information Systems) are concerned with the manipulation and analysis of spatial data at a "Geographic" scale. Apart from issues of storage, database query and visualization, they must deal with several significantly different types of spatial information. These may be roughly classified as: discrete objects; networks; polygonal maps; and surfaces. Each of these has a specific set of assumptions associated with it, a specific data structure, and a specific set of algorithms. This produces a high level of complexity in the construction, manipulation, analysis and comparison of these datasets. This paper reports the results of an attempt to integrate these based on a slight modification of the fundamental spatial query: "What is here?" where "here" is usually an (x, y) location. It summarizes our previous work on this topic, and presents the "big picture" for GIS. We demonstrate that when "here" is replaced by "closest to here" the resulting proximal query (a Voronoi diagram) may be used to manipulate the four categories described above, with a resulting simplification of the system. All discrete objects become "fields", with a value at any location. The catch is that in order to represent non-point objects a line-segment Voronoi diagram is required, and this has been shown to be extremely complex to construct on digital computers. Nevertheless, with the availability of several potential solutions, including our own, we can show the implementation of a basic GIS with a common data structure and set of operations. In addition, several other "awkward" spatial queries can be shown to be simplified.