edited by Stewart Sutherland, Leslie Houlden, Peter Clarke, Friedhelm Hardy
Routledge, 1988
Buku Referensi
prepared by the Cartographic Department of the Clarendon Press
Oxford University Press, 1972
Buku Referensi
Euromonitor, 1989
Buku Teks
Todaro, Michael P.
Longman, 1989
Buku Teks
Euromonitor International, 2003
Buku Referensi