The changing profile of a city in the United States is apparent in the shiftingdefinitions used by the United States Bureau of the Census. In 1870 the censusofficially distinguished the nation's "urban" from its "rural" population for the firsttime. "Urban population" was defined as persons living in towns of 8,000 inhabitantsor more. But after 1900 it meant persons living in incorporated places having 2,500 ormore inhabitants.Then, in 1950 the Census Bureau radically changed its definition of urban to takeaccount of the new vagueness of city boundaries. In addition to persons living inincorporated units of 2,500 or more, the census now included those who lived inunincorporated units of that size, and also all persons living in the densely settled urbanfringe, including both incorporated and unincorporated areas located around cities of50,000 inhabitants or more. Each such unit, conceived as an integrated economic andsocial unit with a large population nucleus, was named a Standard MetropolitanStatistical Area (SMSA).Each SMSA would contain at least (a) one central city with 50,000 inhabitants ormore or (b) two cities having shared boundaries and constituting, for general economicand social purposes, a single community with a combined population of at least 50,000,the smaller of which must have a population of at least 15,000. Such an area wouldinclude the county in which the central city was located, and adjacent counties thatwere found to be metropolitan in character and economically and socially integrated
with the county of the central city. By 1970, about two-thirds of the population of the
United States was living in these urbanized areas, and of that figure more than half
were living outside the central cities.
While the Census Bureau and the United States government used the term SMSA
(by 1969 there were 233 of them), social scientists were also using new terms to
describe the elusive, vaguely defined areas reaching out from what used to be simple
"towns" and "cities." A host of terms came into use: "metropolitan regions," "polynucleated
population groups," "conurbations," "metropolitan clusters," "megalopolises" and so on
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