The diagram represents an ideal construction of the tendencies of any town or city to expand radially from its CBD or the loop. Here is found the greatest density and mobility of population. Encircling the downtown area is the zone of transition. It is in this ecological area (composed of warehouses and slums) that vice, poverty, depersonalization, and social disorganization are most pronounced.

Beyond the zone of transition is the zone largely populated by the working-class families. This was a primary residential area composed of second-generation immigrants who still found their employment in the centre of the city but had been able to escape from the zone of transition.
Still further towards the periphery of the city we find residential zone populated largely by middle-class persons living either in single dwelling or well-maintained apartment buildings. Finally comes the suburban zone composed of economically advantaged, geographically stable, upper-class commuters to the city.