James E Davis, colsultan
Graphic Learning,, 1978
Buku Referensi
C. S. Hammond and Company
C.S. Hammond & Co., [date of publication not identified]
Buku Teks
C.S. Hammond , 1961
Buku Referensi
Lye, Keith, author
The Royal Geographical Society, 2000
Buku Referensi
Wiegand, Patrick
Oxford University Press, 1994
Buku Teks