Diagnosing Spatial Supply–Demand Imbalances in Community Service Facilities Using Banded Isochrone Time-Decay Weighting and Multilevel Benchmarking: A Grid-Level Analysis of Gangdong-Gu, Seoul

Conventional assessments count facilities within binary service areas and evaluate districts against a single citywide average. This study presents a reproducible geospatial diagnostic workflow integrating road-network isochrones at 50–200% of facility-specific base travel times, banded (four-band, piecewise-constant) exponential time-decay weighting of accessible supply, composite effective demand from residential, de facto, and worker populations on a 250 m grid, and multilevel benchmarking against the Seoul average, 25 districts, regional life zones, and three reference districts. Applied to Gangdong-gu, Seoul (452 grids; 71 configured and 45 grid-analyzed facility types), the weighting attenuates accessible supply relative to binary counting within a bounded range (theoretical maximum 15–18%, set by the outermost band; 5.7% observed for libraries) without changing which facilities are counted. Relative provision shifts with the reference group, and intra-district disparities persist beneath district means. Global Moran’s I is positive and significant for 10 of 12 categories; exploratory local indicators identify a candidate shortfall cluster in the Godeok–Gangil area, 11 of whose 17 grids are interior, and shortfalls compound across facility types. Classifications are stable under ±50% perturbation of the decay coefficient. The results are a 2022–2024 snapshot; the framework is an internally examined decision-support workflow, not a new floating catchment area variant.