Accessibility Analysis
Also known as: Hansen Accessibility, Gravity Accessibility Measure, Potential Accessibility, Spatial Accessibility Index
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.
Key highlights
- Reduces the complex geometry of land use and transport into one interpretable score per location.
- Flexible family: gravity, cumulative-opportunity, and floating-catchment variants suit different questions and data.
- Directly supports equity analysis by revealing who can and cannot reach essential services.
- Grounded in the same spatial-interaction theory as gravity and discrete-choice travel-demand models.
Intuition
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How it works
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When to use it
Use accessibility analysis when you want to quantify and compare how well locations connect to opportunities — for evaluating transport investments, siting facilities, assessing equity of access to services, or modelling land-use potential. The gravity form is appropriate when distance decay matters and travel-cost data are available; the cumulative-opportunity form when a clear time threshold is meaningful and simplicity is valued; the floating-catchment form when supply is limited and competition for it must be represented. It is less suitable when the impedance function cannot be credibly calibrated, when opportunity sizes are unknown, or when individual time-budget and scheduling constraints dominate, in which case time-geographic (space-time) accessibility is preferable.
Strengths & limitations
- Reduces the complex geometry of land use and transport into one interpretable score per location.
- Flexible family: gravity, cumulative-opportunity, and floating-catchment variants suit different questions and data.
- Directly supports equity analysis by revealing who can and cannot reach essential services.
- Grounded in the same spatial-interaction theory as gravity and discrete-choice travel-demand models.
- Results hinge on the impedance function and its decay parameter, which must be calibrated and are rarely universal.
- Aggregate, place-based measures ignore individual differences in mobility, schedules, and perceived cost.
- Sensitive to the spatial resolution of origins and destinations and to the modifiable areal unit problem.
- Opportunity counts assume destinations are substitutable, which may not hold for specialized services.
Common pitfalls
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Applications
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Frequently asked
How is accessibility analysis related to the gravity model of migration?
They share the same spatial-interaction core. The gravity model predicts flows between every origin–destination pair; gravity-based accessibility sums one origin's interaction potential with all destinations into a single score. In fact Hansen accessibility is the destination-weighted, impedance-discounted denominator that appears inside a gravity flow model, so accessibility is the 'potential' and the gravity model turns that potential into realized flows.
What is the difference between cumulative-opportunity and gravity accessibility?
Cumulative-opportunity accessibility counts every opportunity within a fixed travel-time threshold equally and ignores everything beyond it, giving a simple, communicable measure. Gravity accessibility instead weights every opportunity by a smooth distance-decay function, so nearer opportunities count more and there is no hard cutoff. Gravity is more behaviourally realistic; cumulative-opportunity is more transparent.
When should I use the two-step floating catchment area method?
Use 2SFCA when the supply of a service is limited and people compete for it — most commonly healthcare. Plain gravity accessibility can credit a location with abundant access even if every nearby clinic is overwhelmed by demand; 2SFCA first computes each provider's supply-to-population ratio and then aggregates those ratios, so it captures crowding and is the standard tool for measuring spatial access to constrained services.
Sources
- 1.Hansen, W. G. (1959). How accessibility shapes land use. Journal of the American Institute of Planners, 25(2), 73–76.
- 2.Isard, W. (1960). Methods of Regional Analysis: An Introduction to Regional Science. MIT Press.ISBN 9780262090032
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Cite this page
ScholarGate. (2026, June 22). Accessibility Analysis. ScholarGate. https://scholargate.app/human-geography/accessibility-analysis