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.