Reilly's law of retail gravitation
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In economics, Reilly's law of retail gravitation states that larger cities will have larger spheres of influence than smaller ones, meaning people travel farther to reach a larger city.
The law presumes the geography of the area is flat without any rivers, roads or mountains to alter a consumer's decision of where to travel to buy goods. It also assumes consumers are indifferent between the actual cities.
The law was developed by William J. Reilly in 1931.
A plain English paraphrase would be that the balance or Break Point () is equal to the Distance () between two places, divided by the following: Unity or Total () plus the Square Root of, the size of Place One () divided by the size of Place Two ().
is distance and and are the sizes of the places between which the distance exists; the answer will give the distance from , also called a break-point. What is the break-point? As an example: after leaving a store a you remember something that you wanted to buy; it just so happens that you are headed towards an alternative store b. The break-point can be thought of as the point after which you would travel towards store b instead of store a because of its notional "gravity". This would happen sooner, for example, if store b is an equivalent store but with greater square footage, suggesting that you are more likely to go to store b for greater available utility. This notional gravity can be influenced by a number of things, but square footage is simple and effective.
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