One of the most powerful analysis capabilities in ArcInfo is the path finding, or routing, commands of the NETWORK module. It is not always an elementary task, however, to use the module for deriving or updating paths that are real-world solutions to various routing problems. Its successful use presumes the GIS specialist understands both the network data model and how it needs to be manipulated for a particular routing application. This paper discusses how to prepare and manage data elements critical to the model. Issues include the management of turntables, modeling one-way and multiple-pass streets, and contending with the "stops-only-at-nodes" requirement. Spatial ordering versus a user-interactive approach is also discussed for defining zones to determine multiple routes.
The George Department of Transportation's (GDOT) Planning Data Services road characteristics database (RCFILE) and their digital road maps include enough information to implement a dynamic segmentation model. The RCFILE contains more than twenty events stored by milepoint along each route. Events such as surface types and bridges are stored in the RCFILE. The link between the RCFILE and the digital map base enables a direct placement of the RCFILE's events, with some restructuring, onto the digital road map. County road maps produced by the GDOT contain such information as surface type and bridge locations. By using the information in the RCFILE and the digital road map, a route system was built and calibrated to the intersection level. This paper covers the procedures used in creating the routes, placing calibration labels, calibrating the routes, and restructuring the RCFILE into more useable event tables. The problems that occurred will be discussed along with work-arounds and solutions.
This paper explores the application of ArcInfo GIS in transportation modeling, with a particular emphasis placed on traffic analysis zone splitting and its centroid connector coding. ArcInfo GIS can be used in the zone splitting process by establishing a correspondence table between old zone and new zone. If a new zone is entirely (100%) in an old zone, polygon analysis (INTERSECT) can be applied to old and new zone coverages. If an old zone entirely (100%) in new zone, the new zone has 100 percent of old zone socioeconomic characteristics. Most often, anew zone overlaps with many old zones in various ways. Under this circumstance, the new zone should be intersected with all old zones, and the percentage share of each common area over each old zone can be calculated. In the post-processing step, the products of each percentage share with each old zone socioeconomic characteristics can be summed up to yield socioeconomic characteristics for each new zone. ArcInfo GIS is extremely helpful in coding zone centroid connectors as well. A point coverage of population and employment densities may be overlaid on the top of polygon coverage of traffic analysis zone to determine the proper zone centroid location. Ideally, a zone centroid should be connected with all links surrounding the zone. In reality, however, some centroid connectors should be excluded due to different physical barriers (rivers, railroads, mass transit facilities, and other line features). By overlaying these line features on the top of polygon feature (TAZ), we might be able to better determine those most reasonable centroid connectors. A zone centroid should not be connected with an intersection node of highway network because of the requirement for determining truing movement. To prevent this situation from happening, in ARCEDIT, a node-to-node snapping distance should be set to zero, and only node-to-arc coding is performed. In addition, polygon manipulation analysis might be conducted to adjust zone boundaries due to various reasons, such as heterogeneous socioeconomic characteristics within the zone and new highway functional classification, and so on.