United States. Central Intelligence Agency
Macmillan, 1993
Buku Referensi
Fryer, D.W.
McGraw-Hill, 1965
Buku Teks SO
by International Monetary Fund
International Monetary Fund, 1999
Buku Teks SO
Schultz, Theodore W.
The Minchigan of Univ. Press, 1966
Buku Teks
prepared by the Cartographic Department of the Clarendon Press
Oxford University Press, 1972
Buku Referensi