De Blij, Harm J., author
John Wiley & Sons, 1997
Buku Teks
Griffin, Paul F., author
Fearon, 1965
Buku Teks
Israel, Saul, author
Holt, Rinehart and Winston, 1976
Buku Teks
Haggett, Peter, author
Prentice-Hall, 2001
Buku Teks
Haggett, Peter, author
Harper & Row, 1975
Buku Teks