An Application of the Grid-Based Two-Step Floating Catchment Area Method to Assess the Spatial Accessibility of Green Spaces in Seoul, South Korea

The conventional Two-Step Floating Catchment Area (2SFCA) method treats large-scale facilities as single centroids, leading to systematic under- and overestimation of spatial accessibility measures. To address this limitation, this study proposes a Grid-based G2SFCA methodology that disaggregates supply facilities into grid cells to better capture their shape and assigns them as multiple access points. Using green spaces in Seoul, South Korea, as a case study, we compared the measures from the proposed method with the conventional centroid-based approach using descriptive statistics and spatial inequality indices. The results indicate that the grid-based method significantly stabilized the distribution, nearly halving the standard deviation and reducing the Gini coefficient. In addition, our proposed method corrected the centroid-induced overestimation of accessibility and provided a more precise identification of underserved areas. By resolving the supply-side centroid problem, our study provides a more robust and realistic foundation for assessing spatial equity in urban planning and resource allocation.