Estimated Population Exposure Within Designated Hazard Zones Across Walkability-Based Urban Spatial Characteristics in Japan: A Nationwide Analysis of Postcode-Level Population Core Cells

While Japan’s population is declining overall, some areas remain densely populated within designated hazard zones. Understanding how these spatial patterns vary across urban contexts is important for sustainable and resilient urban development. This study presents a nationwide analysis of hazard-specific estimated population exposure at postcode-level population core cells across walkability-based urban spatial characteristics in Japan. We integrated designated hazard-zone layers from the Geospatial Information Authority of Japan (GSI) with 250 m census population grids and linked the resulting dataset to the Japan Postcode-level Walkability Index using these core cells as a common spatial unit. This analysis used postcode-level population core cells and was not designed to estimate total hazard-zone-based exposure within entire postcode areas. The four hazard-zone layers were analyzed separately to characterize hazard-specific patterns, not to assess simultaneous or compound hazard events, cumulative exposure, or compound risk. Population core cells in higher-JPWI strata generally overlapped more frequently with flood, storm surge, and tsunami inundation zones, whereas lower-JPWI population core cells overlapped more frequently with designated landslide warning zones. Where hazard-zone overlap was identified, estimated exposed populations tended to be larger in higher-JPWI core cells. The pattern should be interpreted descriptively because the estimate is partly influenced by cell population and JPWI includes a population-density component. Overall, the results show hazard-specific differences in how walkability-based urban spatial characteristics coincide with hazard-zone-based estimated population exposure, providing a transparent and nationally consistent baseline for characterizing designated hazard-zone overlap and estimated exposed population at population core cells in Japan.