Beyond the 15-Minute Circle: From Nominal Coverage to Effective and Equitable Access to Community Health Service Centers for Older Adults in Central Nanjing

Population aging has increased demand for walkable community healthcare for older adults. Using the six central districts of Nanjing as a case study, this study examines whether nominal 15 min access to community health service centers (CHSCs) translates into effective and equitable spatial access after accounting for pedestrian-network barriers, distance decay, and population competition. Based on the 2024 official CHSC roster (n = 60), a census-calibrated 100 m population grid, and an OpenStreetMap walking network, we computed walking times from 500 m hexagonal origins at 1.0 m/s. Binary coverage was compared with equal-supply Gaussian two-step floating catchment area accessibility, and population-weighted Lorenz–Gini measures were calculated overall and among covered older residents. Among 581,474 residents aged 65 years and older, only 28.1% could reach a CHSC within 15 min; 24.8% of covered residents fell below the first quartile of competition-adjusted accessibility. The weighted Gini coefficient was 0.861 overall and 0.506 among covered residents, and high-demand, low-effective areas contained 37.9% of the older population. Under the stated assumptions, the results indicate that nominal proximity overstates modeled equal-supply CHSC accessibility and that joint assessment of coverage, accessibility, conditional equity, and spatial typology can better screen areas for subsequent capacity audits, facility-siting assessment, or pedestrian-network improvement.