Concept analogous to that of market in economy; supply and demand for services meet and exchange in places privileged for their accessibility, which are places.

1. In a network, it characterises the position of nodes in terms of accessibility (see centrality index), the centre being the place endowed with maximal accessibility;

2. For a city, it measures the importance of urban centres in function of the importance of services they provide to customers from outside, i.e. which do not satisfy only the needs of the resident population.

See also: urban functions