Catchment area
The area that can be reached from a point within a given travel time or distance, following the real network rather than a straight line.
A catchment area, in German Einzugsgebiet, is the area reachable from a starting point within a set travel time or distance, by a given mode of transport. It answers the question a circle on a map only pretends to answer: not how far away is this in a straight line, but where can people actually get to.
The difference matters more than it sounds. A circle with a 1,000 metre radius includes places on the other side of a railway line, a motorway or a river with no crossing. A catchment area follows streets, paths and transport routes, so those places fall outside it, correctly. Barriers are exactly what planners need to see, and a circle hides them.
Catchment areas are the basis of most accessibility work. How many residents live within a fifteen minute walk of this school. Which neighbourhoods a new bus stop would serve. Whether a proposed site is reachable by bike from the areas it is meant to serve. In GOAT the tool is called Catchment Area, and it covers walking, cycling, public transport and car.