The Office of Management and Budget defines the area as the Washington � Arlington � Alexandria, DC � VA � MD � WV Metropolitan Statistical Area, a metropolitan statistical area used for statistical purposes by the United States Census Bureau and other agencies. The area includes as its principal cities Washington as well as the Virginia cities of Arlington and Alexandria. The Office of Management and Budget also includes the metropolitan statistical area as part of the larger Baltimore � Washington Metropolitan Area, which has a population of over 8.55 million.
The area is also sometimes referred to as the National Capital Region, particularly by federal agencies such as the Department of Homeland Security. The area in the region that is surrounded by Interstate 495 is also referred to as the "Capital Beltway". The Virginia portion of the area is known as Northern Virginia.
The Washington Metropolitan Area is the most educated and by some measures, the most affluent metropolitan area in the United States. , the population of the Washington Metropolitan Area was estimated to be 5,582,170 (+16.39%), making it the seventh-largest metropolitan area in the country.