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	Accessibility Analysis	Gravity Model of Migration
Ämnesområde	Human Geography	Human Geography
Familj	Process / pipeline	Regression model
Ursprungsår	1959	1946
Upphovsperson	Walter G. Hansen	George Kingsley Zipf (formalized); analogy to Newton's law of gravitation
Typ	Spatial index of the ease of reaching opportunities from a location	Spatial-interaction regression model for migration flows
Ursprungskälla	Hansen, W. G. (1959). How accessibility shapes land use. Journal of the American Institute of Planners, 25(2), 73–76.	Zipf, G. K. (1946). The P1 P2 / D hypothesis: On the intercity movement of persons. American Sociological Review, 11(6), 677–686.
Alias	Hansen Accessibility, Gravity Accessibility Measure, Potential Accessibility, Spatial Accessibility Index	Migration Gravity Model, Demographic Gravity Model, Zipf P1P2/D Model, Gravity Model of Spatial Interaction (Migration)
Närliggande	4	4
Sammanfattning	Accessibility analysis measures how easily opportunities — jobs, shops, clinics, parks — can be reached from a given location, combining the attractiveness (size) of destinations with the cost of travelling to them. The gravity-based formulation introduced by Walter Hansen in 1959 sums the opportunities at all destinations, each discounted by a distance-decay function of travel cost, producing a single accessibility score per origin that has become a foundational concept in transport geography and urban planning.	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.