Central Places in Urban Areas
The spatial organization of cities tends to follow a central places structure as the goal is to provide a hierarchy of services to the whole urban population. This is particularly the case when looking at large metropolitan areas composed of a variety of nodes where commercial and service activities are concentrated. It is assumed that the hierarchy observed at the regional level will also have a correspondence within a metropolitan area. The above example depicts a concentric multi-nodal city with a ring road. Many metropolitan areas in North America, Europe and Asia have such a spatial structure, but with significant variations in density, modal preferences and spatial extension. The Central Business District (CBD) has the highest order and represents the "central place" of an urban area, followed by centers of lesser importance, up to local centers offering basic services including groceries, banking and entertainment. The whole spatial organization is structured by transport axis radiating from the CBD. Increased mobility, namely the automobile, has substantially reduced the cohesion of urban areas and their service hierarchies. Still, although more diffuse, this hierarchy remains present.