Urban areas are densely populated areas where agriculture is not the primary industry. A rural area is a sparsely populated area outside of a major urban or metropolitan area. Rural areas usually rely heavily on agriculture. A suburb is an area that lies outside of an urban area but within a metropolitan area.
The United States Census Bureau recognizes only urban and rural areas, and assigns specific population requirements to them for classification purposes. An urban area is an area in which the population is greater than 50,000 people, or an area in which the population is between 2,500 and 50,000. A rural area is defined as an area of less than 2,500 people. Suburbs, however, are geographically defined as pockets of populations in the outlying areas of large urban centers. Suburbs are usually classified as urban due to populations of greater than 2,500 and their lack of agricultural focus, though suburbs typically do have open land in the form of parks. Suburbs are typically bedroom communities from which people commute into the larger urban centers for employment purposes. An urban center along with its surrounding suburbs forms a metropolitan area. Many cities grow until they combine and become a megalopolis, which is a large densely populated region covering hundreds of miles.