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	Modifiable Areal Unit Problem	Accessibility Analysis
Field	Human Geography	Human Geography
Family	Process / pipeline	Process / pipeline
Year of origin	1984	1959
Originator	Stan Openshaw	Walter G. Hansen
Type	Source of bias and sensitivity in the analysis of spatially aggregated data	Spatial index of the ease of reaching opportunities from a location
Seminal source	Openshaw, S. (1984). The Modifiable Areal Unit Problem. Concepts and Techniques in Modern Geography No. 38. Geo Books, Norwich. ISBN: 9780860941347	Hansen, W. G. (1959). How accessibility shapes land use. Journal of the American Institute of Planners, 25(2), 73–76.
Aliases	MAUP, Scale and Zoning Effect, Aggregation Problem	Hansen Accessibility, Gravity Accessibility Measure, Potential Accessibility, Spatial Accessibility Index
Related	4	4
Summary	The modifiable areal unit problem (MAUP) is the finding that statistical results computed on spatially aggregated data depend on the arbitrary choice of how space is divided into zones. Stan Openshaw's 1984 monograph crystallized the issue into two intertwined components — a scale effect, where results change as data are grouped into larger or smaller units, and a zoning effect, where results change when the boundaries are redrawn at a fixed scale. Because the units used in geography (census tracts, districts, grid cells) are almost always modifiable rather than natural, almost every aggregate spatial statistic is potentially an artefact of its zonation.	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.