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	Nearest Neighbour Index	Accessibility Analysis
Ämnesområde	Human Geography	Human Geography
Familj	Process / pipeline	Process / pipeline
Ursprungsår	1954	1959
Upphovsperson	Philip J. Clark & Francis C. Evans	Walter G. Hansen
Typ	Summary statistic for the degree of clustering or dispersion in a point pattern	Spatial index of the ease of reaching opportunities from a location
Ursprungskälla	Clark, P. J., & Evans, F. C. (1954). Distance to nearest neighbor as a measure of spatial relationships in populations. Ecology, 35(4), 445–453.	Hansen, W. G. (1959). How accessibility shapes land use. Journal of the American Institute of Planners, 25(2), 73–76.
Alias	Clark-Evans Index, Nearest Neighbour Analysis, NNI	Hansen Accessibility, Gravity Accessibility Measure, Potential Accessibility, Spatial Accessibility Index
Närliggande	4	4
Sammanfattning	The nearest neighbour index, introduced by Clark and Evans in 1954, is a simple summary statistic that quantifies whether a set of points is clustered, randomly scattered, or evenly dispersed across an area. It compares the average distance from each point to its closest neighbour with the average distance that would be expected if the same number of points were placed completely at random. The ratio of observed to expected distance, together with a significance test, gives a single interpretable number that has become a staple of point-pattern analysis in geography and ecology.	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.