A city is a relatively large, dense, permanent, heterogeneous, and politically autonomous settlement whose population engages in a range of nonagricultural occupations. Definitions of cities and their associated phenomena vary by time and place, and by population size, area, and function (Shryock, Siegel, and associates 1976, pp. 85–104). The city is often defined in terms of administrative area, which may be larger than, smaller than, or equal to the area of relatively dense settlement that comprises what is otherwise known as the city proper. The suburb is a less dense but permanent settlement that is located outside the city proper and contains populations that usually have social and economic ties to the city.

Definitions of urban vary by nation; in the United States the term refers to populations of 2,500 or more living in towns or cities and to populations living in urbanized areas, including suburbs. In other nations, the lower...