Competition for land and resources within cities eventually leads to separation of urban space into zones with the more desirable zones imposing higher rent. As residents of a city become more affluent, they move outward from the city center. Park and Burgess refer to this a succession, a term also used in plant ecology. They predicted that cities would form into five concentric rings with areas of social and physical deterioration concentrated in the center and prosperous areas near the city's edge. This model is known as concentric zone theory, it was first published in "The City" (1925).