Concentric zone model
In demography, the concentric zone model of a city was put forth by Robert E. Park, Ernest W. Burgess, and Roderick D. McKenzie in The City (1925). Also known as the bull's eye model, the concentric zone model holds that a city begins with a business district surrounded by a transition zone filled with low-income, high-crime area. Outside of that is a working-class residential zone, then a middle-class residential zone, and finally an upper-class residential zone.
The concentric zone model was later criticized for being simplistic and for failing to accurately describe cities other than Chicago, where Park, Burgess, and McKenzie did their original research. Homer Hoyt modified it in the sector model.
The model's five rings do not apply as well in modern times, and even less in European cities. The reason for this is where two settlements grow and meet, the modern and desirable housing is in the centre of the conurbation, and the two former CBDs are at the edges. This problem can be overcome by simply placing two models alongside one another, and merging the high-class residential outer ring where they meet.
Also, in some areas, such as Cheltenham in England, the more desirable and expensive housing (due to more history and heritage) is in the area defined as 'low-class residential'.