edited by Alan Lightman
Houghtn Mifflin, 2000
Buku Teks
Nendeln : The Association of American Geographers
Majalah, Jurnal, Buletin
Katheleen Norris
Houghton Mifflin, 2001
Buku Teks
edited by Elizabeth Hardwick
Ticknor and Fields, 1986
Buku Teks
Cambridge Cambridge University Press 1987,
Buku Teks