
A measure of the nearness or accessibility of a given mass of people to a point. The term is derived from social physics and the concept is closely related to the gravity model, in that it relates mass (population) to distance, but whereas the gravity model deals with the separate relationships between pairs of points, population potential encompasses the influence of all other points on a particular one. The potential exerted on a point (Vi) is defined as:
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where Pj is the population at the jth point, dij is the distance between points i and j, and summation is over all k points. (Most measures of potential include Pi and estimate dij where i = j.) The population potential at point i is thus the sum of the ratios of populations at all points to the distances from i to those points (dij may be raised to some power to incorporate the frictions of distance; see distance decay). Isopleth maps of population potentials have been produced at various scales, to indicate spatial variations in general accessibility (see isolines). Population may be replaced by, for example, purchasing power (Pj becomes PPj) to give a measure of the market potential â€” accessibility to customers â€” at point i.Â (PEO)
Suggested Reading Stewart, J.Q. and Warntz, W. 1968: The physics of population distributions. In B.J.L. Berry and D.F. Marble, eds, Spatial analysis: a reader in statistical geography. Englewood Cliffs, NJ and London: PrenticeHall, 13046. 
