Map - Enplanements at Large Air Traffic Hubs: 1975 and 1999

NOTE: These data include hubs that were classified as large hubs in either 1975 or 1999 or in both years. A large hub is a geographic area that enplanes 1 percent or more of nationally enplaned passengers. A hub may include more than one airport.

SOURCES: Civil Aeronautics Board, Airport Activity Statistics: Twelve Months Ending December 31, 1975 (Washington, DC: 1976); U.S. Department of Transportation, Bureau of Transportation Statistics, Office of Airline Information, Airport Activity Statistics of Certificated Air Carriers, Summary Tables, Twelve Months Ending December 31, 1999 (Washington, DC: 2001).