The central-place classificatory system is an important tool in state and regional planning, and is laid down in spatial structure plans. In addition to supplying the needs of its own population, a central place performs service and development functions for the population of its catchment area. The central place system constitutes a hierarchy of basic, lower-order or small centres, middle-order centres, and high-order centres as determined at the different levels of state spatial planning. Some states insert intermediate categories in the hierarchy. Depending on their assignment to a central place, catchment areas are defined as local, intermediate or extended areas.