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	Reilly's Law of Retail Gravitation	Huff Model
Field	Human Geography	Spatial analysis
Family	Regression model	Regression model
Year of origin	1931	1964
Originator	William J. Reilly	David Huff
Type	Deterministic gravity model of retail trade-area delineation	Probabilistic spatial interaction model
Seminal source	Reilly, W. J. (1931). The Law of Retail Gravitation. Knickerbocker Press, New York.	Huff, D. L. (1964). Defining and estimating a trading area. Journal of Marketing, 28(3), 34–38.
Aliases	Law of Retail Gravitation, Reilly's Retail Gravitation Model, Retail Breaking-Point Model, Reilly Gravity Model	Huff Gravity Model, Probabilistic Retail Gravity Model, Huff Trade Area Model, Huff Çekim Modeli
Related	4	3
Summary	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.	Proposed by David Huff in 1964, the Huff Model is a probabilistic spatial interaction model that estimates the likelihood that consumers located in a given geographic zone will choose to shop at a particular retail outlet. It extends deterministic gravity models by assigning each consumer zone a probability of patronage across all competing stores, weighting store attractiveness (typically measured by floor area) against the friction of travel time or distance. The model is widely used in retail site selection, trade area delineation, and market share forecasting.