The U.S. Census Bureau classifies areas as urban or rural based on population size and density.
- population density: The average number of people who live on each square mile (or kilometer) of land.
Different international, national, and local agencies may define “urban” in various ways. For example, city governments often use political boundaries to delineate what counts as a city. Other definitions may consider total population size or population density. Different definitions may also set various thresholds, so that in some cases, a town of just 2,500 may count as an urban city, whereas in other contexts, a city may be defined as having at least 50,000 people. Other agencies may define “urban” based on land use: places count as urban if they are built up with residential neighborhoods, industrial sites, railroad yards, cemeteries, airports, golf courses, and similar areas. Using this sort of definition, in 1997, the U.S. Department of Agriculture tallied over 98,000,000 acres of “urban” land.
In spite of these competing definitions, in the United States “urban” is officially defined following guidelines set by the U.S. Census Bureau. The Census Bureau defines “urban areas” as areas with a population density of at least 1,000 people per square mile and at least 2,500 total people. Urban areas are delineated without regard to political boundaries. Because this definition does not consider political boundaries, it is often used as a more accurate gauge of the size of a city than the number of people who live within the city limits. Often, these two numbers are not the same. For example, the city of Greenville, South Carolina has a city population under 60,000 and an urbanized area population of over 300,000, while Greensboro, North Carolina has a city population over 200,000 and an urbanized area population of around 270,000. That means that Greenville is actually “larger” for some intents and purposes, but not for others, such as taxation, local elections, etc.
As of December, 2010, about 82% of the population of the United States lived within the boundaries of urbanized area. Combined, these areas occupy about 2% of the land area of the United States. The majority of urbanized area residents are suburbanites; core central city residents make up about 30% of the urbanized area population (about 60 million out of 210 million). In the United States, the largest urban area is New York City, with over 8 million people within the city limits and over 19 million in the urban area. The next five largest urban areas in the United States are Los Angeles, Chicago, Washington, D.C., Philadelphia, and Boston.
American urban areas by size: This map shows major urban areas in America.