Urban modeling in computer-graphic and geographic information system environments

Computer graphics and its broader application as visualization are at last beginning to have an impact on the ways analysts and model builders articulate and communicate their intellectual understanding of urban systems. Geographic information systems (GIS) lie in the vanguard of these developments and there is presently much effort in linking these systems to traditional spatial models so that the power of GIS databases and display capabilities can be harnessed. To demonstrate the import of these ideas, a prototypical visual environment has been developed for such modeling and in this paper it is shown how it can be implemented. The elements of such visualization are first defined in terms of the model-based processes which characterize applications, emphasizing data exploration, model calibration, prediction, and prescription. These processes are then concentrated through model inputs, outputs, and causal structures, illustrating the operation of various model sectors through different modes of spatial statistical and graphic analysis. These ideas are implemented through windowing systems which mix text, numerics, and graphics, and are illustrated using an elementary model of residential location of Melbourne, Australia. The operation of the model in a UNIX environment which is accessed through proprietary windows-based software is demonstrated, thus providing a platform to discuss the problems of linking conventional model-based techniques to graphics software in general, GIS in particular. The paper is concluded with a sketch for future work.