Transportation
In transportation, accessibility refers to the ease of reaching destinations. Academics have disputed how the term "ease" should be defined and measured. People who are in places that are highly accessible can reach many other activities or destinations quickly, people in inaccessible places can reach fewer places in the same amount of time.
A measure that is often used is to measure accessibility in a traffic analysis zone i is: 
where:
- = index of origin zones
- = index of destination zones
- = function of generalized travel cost (so that nearer or less expensive places are weighted more than farther or more expensive places).
For a non-motorized mode of transport, such as walking or cycling, the generalized travel cost may include additional factors such as safety or gradient.
Transport for London utilise a calculated approach known as Public Transport Accessibility Level (PTAL) that uses the distance from any point to the nearest public transport stops, and service frequency at those stops, to assess the accessibility of a site to public transport services.
Automobile accessibility also refers to ease of use by disabled people.
Read more about this topic: Accessibility