In human geography: a catchment area is the area and population from which a city or individual service attracts visitors or customers. For example, a school catchment area is the geographic area from which students are eligible to attend a local school. Local governments and community service organizations often define catchment areas or service areas for public safety (e.g., fire and police) and emergency medical services. Catchment areas are generally founded either on formal local government boundaries or else on some other geographic basis. For example, a neighbourhood or district of a city often has several small convenience shops, each with a catchment area of several streets. Supermarkets, on the other hand, have a much lower density, with catchment areas of several neighbourhoods (or several villages in rural areas). This principle, similar to the Central Place Theory, makes catchment areas an important area of study for geographers, economists, and urban planners.