GIS-Based Walking Map Isochrones in Measuring Transit Catchment: A Spatial Approach to Urban Accessibility

Abstract. Transit accessibility is an important element of sustainable urban mobility and is often assessed in transit-oriented development (TOD) design using fixed-distance radial buffers. These methods however tend to oversimplify real-world accessibility by assuming straight-line movement and ignoring physical barriers. This study uses a GIS network-based isochrone method to improve the delineation of transit station catchment regions and examines the effect of the method on accessibility analysis. Walking isochrones of 5, 10 and 15 minutes were used for selected rail transit stations in Klang Valley, Malaysia using open-source geospatial data as well as open-source tools such as QuickOSM and QNEAT3. These were compared with the regularly used standard Euclidean radial buffers of 400 m, 800 m and 1500 m. Within each delineation, we assessed spatial indicators that are catchment area size, population coverage and land use mix. Results show that radial buffers consistently overestimate or occasionally underestimate accessible areas, resulting in inaccurate estimation of catchment area, population coverage or land-use diversity. Catchments based on isochrones tend to be smaller, less regular in shape and more vulnerable to changes in roadway connectivity and physical barriers. These results indicate that relying on radial buffers might lead to false perceptions of transit accessibility and service coverage. This study may guide other cities in more accurate transit accessibility planning using open-source data and replicable GIS techniques. The suggested approach improves the accuracy of service catchment analysis and enables a more context-aware TOD design.