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	Reilly's Law of Retail Gravitation	Central Place Analysis
分野	Human Geography	Human Geography
系統	Regression model	Process / pipeline
提唱年	1931	1933
提唱者	William J. Reilly	Walter Christaller
種類	Deterministic gravity model of retail trade-area delineation	Theory and analytic framework for the size, number, and spacing of settlements
原典	Reilly, W. J. (1931). The Law of Retail Gravitation. Knickerbocker Press, New York.	Christaller, W. (1966). Central Places in Southern Germany (C. W. Baskin, Trans.). Prentice-Hall. (Original work published 1933). ISBN: 9780131226302
別名	Law of Retail Gravitation, Reilly's Retail Gravitation Model, Retail Breaking-Point Model, Reilly Gravity Model	Central Place Theory, Christaller Central Place Model, Settlement Hierarchy Analysis, Central Place Hierarchy
関連	4	4
概要	Reilly's law of retail gravitation is a deterministic model that predicts how an intermediate town's retail trade divides between two larger competing cities. Formulated by William J. Reilly in 1931 by analogy with Newtonian gravity, it states that each city attracts trade in direct proportion to its population and in inverse proportion to the square of the distance to it. Solving for the point of equal attraction yields the famous breaking point — the boundary along the route between two cities where their trade areas meet.	Central place analysis is the study of the size, number, and spacing of settlements as service centres, grounded in Walter Christaller's central place theory of 1933. It explains why settlements form an orderly hierarchy — many small villages, fewer towns, a handful of cities — and why higher-order centres are spaced farther apart and offer more specialized goods, deriving the famous nested pattern of hexagonal market areas from two economic concepts: the range and the threshold of a good.