The unique ability of GIS to handle complex spatial relationships makes it a natural tool to use in the planning and analysis of transportation systems, specifically public transportation systems. The current use of GIS technology in public transit agencies and metropolitan planning organizations (MPOs) for transportation planning and analysis has become more popular and demanding (Schweiger, 1992). One of the most important and accepted application of GIS in transportation planning, is public transit networking and routing. Transit modeling uses a variety of GIS spatial analysis functions for identifying the route, potential location of stops on a transit route, calculating distances between stops or between origin and destination points, calculation of temporal values over those distances, etc. (Choi & Jang, 2000). The transit route location, stop identification and analysis problem requires the estimation of a population within the service area of a route.