The concentric zone model of urban landuse emphasizes centripetal forces that focus economic activity on the CBD which was the dominant center of urban spatial organization in the industrialized city. According to the sector model a city grows outward from a central business district in a series of wedges or sectors, centered on routes of transportation. The multiple nuclei model describes a model in which cities develop around a series of centroids. The land uses are identified in areas around various nucleations in downtown, but especially in the suburbs. No one city represents a pure form of any of the three models.
Most cities have visible aspects of all three models and are therefore composite .
As a result of automobile based interurban dispersal, the city has evolved into a restructured form called multicentered metropolis . Classical models cannot accommodate this new reality easily. In Canada, there is the Windsor-Quebec City axis, known as Main Street . Intercity neighborhood redevelopment involves gentrification - property upgrading by high income settlers which frequently results in the displacement of low income residents. The need for the city, as far as the middle class is concerned, has diminished.