Osol, Arthur, 1905-1988
J. B. Lippincott Company, 1960
Buku Referensi
Risjord, Norman K.
Prentice-Hall, 1985
Buku Teks
Rand McNally and Company.
Rand Mcnally & Company, 2006
Buku Teks
Washington U.S. Department of Health, Education, and Welfare 1955
Buku Teks
United States Information Agency, 1987
Buku Teks