Urbanization

Urbanization is both a historical process and a technical term for describing population distribution. In the latter sense, it refers to an increase in the proportion of a region's or political unit's population who live in cities. It therefore runs between 0 and 100 percent.

The urbanization of the United States has followed the same demographic pattern found in every urbanizing society for the last three centuries. For the first 6,000 years of urban life, no society was long able to maintain an urban percentage greater than 5 to 10 percent. Starting with 18th-century England, however, one nation after another has experienced an accelerating shift from rural to urban population. After several generations of rapid urbanization, the process levels off toward a new equilibrium, in which about three quarters of the population live in cities and many of the rest pursue city-related activities in smaller towns. When the urban proportion of a population is graphed against time, the result is an S-shaped curve that turns up sharply at a takeoff point, rises rapidly for perhaps a century, and then begins to level off.

The shift from rural to urban society involves the appearance of more points or places of concentration and the rapidly increasing population size of certain favored points. This dual process has been especially transparent for the United States, as nearly all the nation's cities have been new establishments by European-origin empires and settlers. Both the northward expansion of the Spanish empire and the westward expansion of the American Republic were accompanied by the planting of new towns, whether by governmental edict or as real estate speculations. The history of urbanization through much of the United States is a story in which multiple town sites in a given region contend for economic growth, with some sites failing to gain any permanent population, others growing into small towns, still others into substantial cities, and a few into economically dominant metropolitan centers.

The progress of urbanization as a demographic or statistical process can be measured by comparing the largest settlements at six “snapshots” equally spaced over time. Table 1 gives the five largest cities in 1800, 1840, and 1880, the five largest metropolitan districts in 1920, the five largest standard metropolitan statistical areas in 1960, and the five largest consolidated metropolitan statistical areas in 2000.

The changing definitions used by the U.S. census reflect the growing size and complexity of urban areas. A simple distinction between an incorporated city and rural territory sufficed for much of the 19th century, although as early as 1880, experts were growing uneasy that municipal boundaries failed to capture the new suburbs and satellite towns surrounding large cities. The response has been a series of “metropolitan” definitions to encompass a core city and closely related adjacent settlements. The terminology in use in 1920 and 1960 assumed the continued prominence of a single, central city. The term consolidated metropolitan area recognizes that some great urban regions have resulted from the intertwining and overlapping of multiple metropolitan areas, such as San Francisco, Oakland, and San Jose.

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