The higher capital investment caused by urbanization brings health and social benefits that could be achieved in rural areas only at far greater costs. The data are sparse and not always reliable, but access to drinking water, sanitation, health services, and educational opportunities is often dramatically higher in urban areas overall than in rural areas. These benefits, however, often do not extend to the poorest groups within a city, as is described below. The steady increase in the level of urbanization worldwide since the 1950s also reflects, to a large degree, the enormous changes in the nature and scale of economic activity worldwide. Urban growth is inextricably linked with economic growth, although it is not entirely clear which fuels which.
Cities provide a natural locus for economic growth.
Commerce and industry concentrate in cities because of the economies of scale they offer. In a self-perpetuating cycle, commerce and industry in turn attract the ancillary services needed to support them. The efficiency inherent in urban areas translates into major gains in productivity. These economies of agglomeration, as they are often called, are especially important when a city's economic base rests on manufacturing. Yet cities have held their allure, even flourished, when the economic base shifts from manufacturing to services such as finance and banking, as it has in much of the developed world.