Geographic information systems (GIS) provide powerful tools for spatial analysis. However, the inherent capabilities of the systems for complex and dynamic analyses remain limited. Simulation models, on the other hand, are powerful tools for complex and dynamic situations. But they often lack the intuitive visualization and spatial-analysis functions that GIS offers. The integration of GIS and simulation models, within a common and interactive graphical user interface, produces more powerful, easy-to-use, and easy-to-understand planning and analysis of information systems.