GIS-T/Conflate, an ArcInfo application, merges highway networks. It was specifically customized for Southern California Association of Governments to merge their Thomas Brothers Base Maps (spatially accurate) with their TRANPLAN transportation model networks (feature rich, not spatially accurate). Due to the disparate purposes for which the files were developed-the Thomas Brothers for mapmaking, the TRANPLAN networks for developing transportation model forecasts-there proved to be no attributes suitable for matching street segments between the two files. Nevertheless, the SCAG networks have been matched over a five county area with a very successful match rate. To give some idea of the magnitude of this task, the base year model network had over 30,000 street segments and the Los Angeles county Thomas Brothers map alone has over 295,000 arcs. The conflated-or merged-networks have been used to prepare presentation maps of transportation model forecasts. The next step for this application will be the confation of SCAG's transportation model transit networks to the Thomas Brothers map.
Traditionally, transportation modeling and GIS-T data analyses have been performed independent of each other using proprietary software programs. Even where the two datasets have been brought together, the data have most often been shown as simple overlays with no real integration between them. Indeed, the two datasets may not be spatially rectified or conflated to allow the data to be integrated. The benefits of integrating model networks and transportation data are widely championed by practitioners but rarely accomplished. The benefits include being able to perform transportation impact studies, evaluate trip generation, mode choice and trip distribution effects, assessment of environmental impacts of planned projects, and the display of transportation model results to visualize forecast traffic impacts. As well as the creation of maps, integrating the datasets enable more powerful data analyses to be performed including buffer analysis and SQL queries of multiple tables in the GIS database. The paper will describe the transportation GIS project implemented by Southern California Association of Governments (SCAG) which integrates the agency's transportation street network, model networks, land use, demographic and employment datasets using ArcView. The datasets are integrated in the SCAG Geographic Data Interface (SGDI). The SGDI provides a user-friendly interface to allow the non-technical GIS user to access, query, display, analyze and plot the transportation and planning data. The integration of all the agency's data in a single uniform environment and in the same map base provides a powerful yet user-friendly GIS application. The presentation will include examples of the type of integrated transportation planning analyses that are now possible using ArcView applications.