APA

International Geographical Congress, . (1990). 27 th international geographical congress. Washington, United States: The U. S. National Committee for Geography.

Chicago

International Geographical Congress, . 1990. 27 th international geographical congress. Washington, United States: The U. S. National Committee for Geography.

Harvard

International Geographical Congress, . (1990). 27 th international geographical congress. Washington, United States: The U. S. National Committee for Geography.

MLA

International Geographical Congress, . 27 th international geographical congress. Washington, United States: The U. S. National Committee for Geography. 1990.