Spatial representation and scale impacts in transit service assessment

There has been much research over the past decade on aspects of bus-transit-system service and performance. Common to studies is the necessity that the population served by systems be estimated. Usually this entails delineating areas for which demand is covered through the use of geographic information systems (GIS), as well as deciding on how best to represent potential ridership spatially. However, little attention has been paid to spatial issues inherent in these choices. Research has emphasized the modeling of transit problems using GIS rather than giving explicit attention to the spatial considerations underlying analyses. To this end, we investigate issues of spatial representation in transit studies. A GIS-based analysis of bus transit for a small urban municipality is utilized to highlight that estimates of service coverage are sensitive to the choice of areal units representing ridership (scale), whether individual stops or routes are used to determine access, and how network versus Euclidean distances affect estimates. As such, spatial representation and modeling sensitivity are evaluated in the context of transit-service provision. The study results suggest that representation issues are critical in evaluating transit access in the context of planning and policy development using GIS.