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	Population Potential Model	Accessibility Analysis
Campo	Human Geography	Human Geography
Famiglia	Process / pipeline	Process / pipeline
Anno di origine	1947	1959
Ideatore	John Q. Stewart	Walter G. Hansen
Tipo	Social-physics measure of the cumulative influence of population at a location	Spatial index of the ease of reaching opportunities from a location
Fonte seminale	Stewart, J. Q. (1947). Empirical mathematical rules concerning the distribution and equilibrium of population. Geographical Review, 37(3), 461–485.	Hansen, W. G. (1959). How accessibility shapes land use. Journal of the American Institute of Planners, 25(2), 73–76.
Alias	Potential of Population, Market Potential Model, Demographic Potential, Stewart Potential	Hansen Accessibility, Gravity Accessibility Measure, Potential Accessibility, Spatial Accessibility Index
Correlati	4	4
Sintesi	The population potential model measures the cumulative influence that all of a region's population exerts on a given point, weighting each place's population inversely by its distance. Introduced by the astronomer-turned-social-scientist John Q. Stewart in 1947 as part of his 'social physics', it borrows the gravitational-potential analogy from physics: every population mass contributes potential at a point in proportion to its size and in inverse proportion to its distance. Summed across all places, the result is a smooth potential surface that maps relative accessibility, market reach, and demographic pressure.	Accessibility analysis measures how easily opportunities — jobs, shops, clinics, parks — can be reached from a given location, combining the attractiveness (size) of destinations with the cost of travelling to them. The gravity-based formulation introduced by Walter Hansen in 1959 sums the opportunities at all destinations, each discounted by a distance-decay function of travel cost, producing a single accessibility score per origin that has become a foundational concept in transport geography and urban planning.