Concentric Zone Model

From the centre outward, Burgess identified five rings: the central business district (the commercial core); the zone in transition, where industry encroaches on deteriorating housing occupied by recent immigrants and the poor; the zone of independent workers' homes; the zone of better residences for the middle class; and the commuter zone of suburbs and satellite towns at the periphery. Social status and housing quality broadly increase with distance from the centre, while density and the share of recent arrivals decrease.

Because the Chicago School explicitly borrowed concepts from biological ecology to explain the city. Burgess treated urban zones like competing species in an ecosystem: groups and land uses compete for territory, and as the centre grows it 'invades' the adjacent zone, whose occupants are displaced outward in a process of 'succession'. Distance from the centre, competition, and invasion-succession give the model its dynamic, organism-like character, which is why it is described as a human-ecology or urban-ecology model rather than a purely economic one.

Not as a literal description of modern cities. It was built on 1920s Chicago — a single-centred, rapidly growing industrial city served by mass transit and walking — and modern cities are often polycentric, car-oriented, planned, or shaped strongly by terrain and history, producing sectoral or multi-nuclei patterns instead of clean rings. Its enduring value is conceptual: it pioneered the systematic study of urban spatial structure, introduced the ecological logic of competition and succession, and still serves as an idealised baseline against which the real, messier geography of a city can be compared.