Urban Landscape

The U.S. Census Bureau defines an urban area as: "Core census block groups or blocks that have a population density of at least 1,000 people per square mile (386 per square kilometer) and surrounding census blocks that have an overall density of at least 500 people per square mile (193 per square kilometer)."
The concept of Urbanized Areas as defined by the U.S. Census Bureau is often used as a more accurate gauge of the size of a city, since in different cities and states the lines between city borders and the urbanized area of that city are often 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 — meaning that Greenville is actually "larger" for some intents and purposes, but not for others, such as taxation, local elections, etc.
The largest urban area in the United States is that of New York City, with its city proper population exceeding 8 million and its metropolitan area population almost 19 million. The next four largest urban areas in the U.S. are those of Los Angeles, Chicago, Miami and Philadelphia. About 79 percent of the population of the United States lives within the boundaries of urbanized area as of April, 2000. Combined, these areas occupy about 2 percent of the United States. The majority of urbanized area residents are suburbanites; core central city residents make up about 30 percent of the urbanized area population (about 60 out of 210 million).
In the U.S. Department of Agriculture's natural resources inventory, urban areas are officially known as developed areas or urban and built-up areas. Such areas include cities, villages, other built-up areas of more than 10 ac (4 ha), industrial sites, railroad yards, cemeteries, airports, golf courses, shooting ranges, institutional and public administration sites, and similar areas. The 1997 national resources inventory placed over 98,000,000 ac (40,000,000 ha) in this category, an increase of 25,000,000 ac (10,000,000 ha) since 1982.