U.S. Department of Commerce, 1987, Codes for the Identification of the States, the District of Columbia and The Outlying Areas of the United States, and Associated Areas (FIPS 5-2): Washington, D.C., National Institute of Standards and Technology.
U.S. Department of Commerce, 1990, Counties and Equivalent Entities of the United States, Its Possessions, and Associated Areas (FIPS 6-4): Washington, D.C., National Institute of Standards and Technology.