Urban structure
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Urban structure is the arrangement of urban areas. Sociologists, economists, and geographers have developed three models to explain where different types of people and businesses tend to exist within the urban setting. These three models are the concentric zone model, the sector model, and the multiple nuclei model.
Concentric Zone Model
This model was the first to explain distribution of social groups within urban areas. It was created by sociologist E. W. Burgess in 1923. According to this model a city grows outward from a central point in a series of rings. The innermost ring represents the central business district. It is surrounded by a second ring, the zone of transition, which contains industry and poorer-quality housing. The third ring contains housing for the working-class and is called the zone of independent workers' homes. The fourth ring has newer and larger houses usually occupied by the middle-class. This ring is called the zone of better residences. The outmost ring is called the commuter's zone. This zone represents those that choose to live in small villages that and commute into the center to work.
Sector Model
A second theory of urban structure was proposed in 1939 by an economist named Homer Hoyt. His model, the sector model, proposed that a city develops in sectors instead of rings. Certain areas of a city are more attractive for various activities, whether by chance or geographic and environmental reasons. As the city grows and these activities flourish and expand outward, they do so in a wedge and become a sector of the city. If a district is setup for high income housing, for example, any new development in that district will expand from the outer edge.
To some degree this theory is just a refinement on the concentric model rather than a radical restatement. Both Hoyt and Burgess claimed Chicago supported their model. Burgess claimed that Chicago's central business district was surrounded by a series of rings, broken only by Lake Michigan. Hoyt argued that the best housing developed north from the central business district along Lake Michigan, while industry located along major rail lines and roads to the south, southwest, and northwest.
Multiple Nuclei Model
Geographers C.D. Harris and E. L. Ullman developed the multiple nuclei model in 1945. According to this model a city contains more than one center around which activities revolve. Some activities are attracted to particular nodes while others try to avoid them. For example, a university node may attract well-educated residents, pizzerias, and bookstores, whereas an airport may attract hotels and warehouses. Other land-use activities that are incompatible will avoid clustering in the same area. This is why heavy industry and high-income housing rarely exist in the same neighbourhood.