The whole notion of “city” versus “suburb” is based on the way the world looked during the first part of the 20th century. Jobs were clustered in dense urban cores. People would live in the residential rings surrounding the city, and commute in to work. The suburbs were “sub“ because they depended economically on the city.
This pattern was reflected in economists’ models of cities. But in the 1980s, urban economists began to realize that cities didn’t have to be shaped like a series of concentric rings. New polycentric models reflected the fact that what we call a city -- greater Houston, or greater Los Angeles -- could in fact be a series of smaller cities, all trading with each other in close proximity, with commuting zones and housing markets that overlapped. Researchers found that by the year 2000, most American cities fit this model better -- jobs were no longer clustered tightly in a central business district, but dispersed throughout sprawling metropolitan areas.
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