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	Spatial Gini Concentration Index	Gravity Model of Migration
Ämnesområde	Human Geography	Human Geography
Familj	Process / pipeline	Regression model
Ursprungsår	1991	1946
Upphovsperson	Corrado Gini (coefficient); locational adaptation in regional science / economic geography	George Kingsley Zipf (formalized); analogy to Newton's law of gravitation
Typ	Descriptive index of how unevenly an activity is distributed across space	Spatial-interaction regression model for migration flows
Ursprungskälla	Duncan, O. D., & Duncan, B. (1955). A methodological analysis of segregation indexes. American Sociological Review, 20(2), 210–217.	Zipf, G. K. (1946). The P1 P2 / D hypothesis: On the intercity movement of persons. American Sociological Review, 11(6), 677–686.
Alias	Locational Gini Coefficient, Spatial Gini Index, Geographic Concentration Index, Gini Index of Spatial Inequality	Migration Gravity Model, Demographic Gravity Model, Zipf P1P2/D Model, Gravity Model of Spatial Interaction (Migration)
Närliggande	4	4
Sammanfattning	The spatial (or locational) Gini concentration index adapts the classic Gini coefficient to geography, summarizing in a single number between zero and one how unevenly an activity — an industry, a population group, a resource — is distributed across spatial units relative to a benchmark such as total population or land area. It is the workhorse measure for quantifying geographic concentration and agglomeration in economic geography.	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.