About 70 percent of Americans live in urban areas, and more than 40 percent are in areas of 1 million people or more. Several elements of urbanization are emphasized in our discussion. Cities have a particular form, a particular layout. Most American cities have a rectangular-grid pattern, partly a result of cultural attitudes, partly a result of a desire for efficient transport before the automobile, and partly because that pattern is an easy way to survey the land. Within cities, there is a collection of industrial and commercial centers, residential areas, warehouses, and so on.
Cities exist for many different reasons.
They may have an important transportation role. Or they may provide an important administrative function. Perhaps they are a center of recreation or manufacturing. Most cities, certainly all large ones, contain many different urban functions. Nevertheless, many are characterized by certain dominant functions that were the reason for their development and much of their early growth, and that today continue to give them their special character.