手法を比較

	Isochrone Analysis	Two-Step Floating Catchment Area
分野	Human Geography	Human Geography
系統	Process / pipeline	Process / pipeline
提唱年	1959	2003
提唱者	Edsger W. Dijkstra (shortest-path foundation)	Wei Luo & Fahui Wang
種類	Computation of travel-time contours reachable from a location on a network	Spatial accessibility measure for competition over constrained services
原典	Dijkstra, E. W. (1959). A note on two problems in connexion with graphs. Numerische Mathematik, 1(1), 269–271.	Luo, W., & Wang, F. (2003). Measures of spatial accessibility to health care in a GIS environment: synthesis and a case study in the Chicago region. Environment and Planning B: Planning and Design, 30(6), 865–884.
別名	Travel-Time Analysis, Isochrone Mapping, Service Area Analysis, Travel-Time Contours	2SFCA, Floating Catchment Area Method, Enhanced Two-Step Floating Catchment Area, 2SFCA Accessibility
関連	4	4
概要	Isochrone analysis computes the area reachable from a location within a given travel time, drawing contour lines — isochrones — that enclose everywhere you can get to in, say, 15, 30, or 45 minutes. It rests on the single-source shortest-path problem solved by Dijkstra's 1959 algorithm: from an origin, the travel time to every node of a routable network is found, thresholded, and converted into a polygon of reachable space. Isochrones turn an abstract travel-time field into an intuitive map of reach, and underpin service-area planning, accessibility measurement, and location analysis.	The two-step floating catchment area (2SFCA) method measures spatial accessibility to constrained services — most famously physicians and hospitals — by accounting not only for how close supply is but for how many other people are competing for it. Introduced by Wei Luo and Fahui Wang in 2003, it works in two passes: first computing a supply-to-demand ratio at every service location, then summing those ratios over all services within reach of each population site. The result is a single accessibility score per location that captures both proximity and crowding, and it has become the standard measure of access to healthcare and other capacity-limited services.