District of Columbia, federal district of the United States, coextensive with the city of Washington, D.C., the national capital. It is situated on the Potomac and Anacostia rivers and has an area of 68 sq mi. It is not a state, nor is it part of any state. It is a "federal district" established by the US Constitution as the seat of government. The site was chosen by George Washington, for whom the city was named. Government departments and agencies are the major source of employment in the District. Other important industries are tourism, including the convention trade; scientific research and development; and the manufacture of technical equipment.