A section of the earth's surface from which surface and ground water flows into a separate river or lake.

Catchment area, a basin, an area bounded by a dividing line on the earth's surface from which water flows to a reservoir. The structure of the surface of the catchment area (relief, presence of lakes and swamps, type of vegetation) has a significant influence on the conditions of water flow. For example, the relief of the catchment area determines the slopes and the density of the network of rivers and gullies, i.e. the rate of runoff along the slopes and the duration of water flow along the channels. The presence of various closed depressions means that part of the water arriving at the surface during the day is delayed in these depressions, where it is used for evaporation and filtration, and only after the depressions have been filled does it begin to flow into the channel.

In human geography, a catchment area is an area from which a place, such as a city, service or institution, attracts a population to use its services and economic opportunities. Catchment areas can be defined on the basis of where people naturally flock to a particular place (for example, the catchment area of a workforce) or as defined by governments or organisations for the provision of services. Governments and public bodies often define catchment areas for planning and public safety purposes, for example to ensure universal access to services such as fire, police, ambulance and hospitals. In business, catchment area is used to describe the influence by which a point of sale attracts its customers. The catchment area of an airport can be used as a basis for assessing the profitability of the route.

Catchment areas can be defined in relation to location and based on a number of factors, including distance, travel time, geographical boundaries or population size within the catchment area. Catchment areas are usually divided into two categories: those that arise organically, i.e. 'de facto', and those places to which people are naturally drawn, such as a large shopping centre. In terms of geography, a catchment area is a low-lying area where water from higher ground is collected in a single reservoir. The sources of water collected can vary from rainwater to snowmelt. Catchment areas may divert their water to other lower basins or, in the case of a closed catchment, to a single location, usually a lake. The catchment area, from the point of view of the place to which people are attracted, can be a town, a service or an institution. Catchment boundaries can be modelled using geographic information systems. The services provided in different catchment areas in the same area can be very different, depending on how and when the catchment areas were created. They are usually contiguous, but may overlap in the description of competing services.