Сравнение на методи

	Two-Step Floating Catchment Area	Gravity Model of Migration
Област	Human Geography	Human Geography
Семейство	Process / pipeline	Regression model
Година на възникване	2003	1946
Създател	Wei Luo & Fahui Wang	George Kingsley Zipf (formalized); analogy to Newton's law of gravitation
Тип	Spatial accessibility measure for competition over constrained services	Spatial-interaction regression model for migration flows
Основополагащ източник	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.	Zipf, G. K. (1946). The P1 P2 / D hypothesis: On the intercity movement of persons. American Sociological Review, 11(6), 677–686.
Други названия	2SFCA, Floating Catchment Area Method, Enhanced Two-Step Floating Catchment Area, 2SFCA Accessibility	Migration Gravity Model, Demographic Gravity Model, Zipf P1P2/D Model, Gravity Model of Spatial Interaction (Migration)
Свързани	4	4
Резюме	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.	The gravity model of migration explains the volume of movement between two places as proportional to the product of their populations (masses) and inversely proportional to the distance separating them, by direct analogy to Newton's law of universal gravitation. Formalized for intercity movement by George Kingsley Zipf in 1946 and embedded in regional science by Walter Isard, it is the workhorse model of human geography for predicting migration, commuting, and other spatial-interaction flows.