Brown, James M., author
Barnes & Noble, 1982
Buku Teks
Sage Publications, Inc, 2005
Majalah, Jurnal, Buletin
edited by Stijn Oosterlynck, Nick Schuermans and Maarten Loopmans.
USA Routledge, 2017
Buku Teks
Tim, Cresswell, author
Wiley , 2015
Buku Teks
Anne Buttimer, David Seamon, editors
Croom Helm, 1980
Buku Teks