At the University of Chicago from the 1910s, Robert Park, Ernest Burgess and their colleagues founded urban sociology, treating the city as a social laboratory and a kind of ecological system. Burgess's 1925 concentric-zone model described the city as a series of rings expanding outward from a central business district through a transitional zone to commuter suburbs. The school combined this ecological theory with detailed empirical fieldwork on immigrants, slums, gangs and city neighbourhoods. Later scholars added the sector and multiple-nuclei models in response.
It produced the first systematic theories of how social groups sort themselves across urban space, shaping decades of work on neighbourhoods, segregation and land use. The concentric-zone diagram became a foundational, much-debated image of urban structure.
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