Gyeszly, Suzanne D.
The Borgo Press, 1994
Buku Referensi
Brown, J. F.
Frederick A. Preager, 1966
Buku Teks SO
Westview Press, 1989
Buku Teks
Westview Press, 1989
Buku Teks
by the Economist Intelligence Unit and the Cartographic Dept. of the Clarendon Press
Oxford University Press, 1956
Buku Referensi