MLA

of Engineers, United States. Army. Corps. Strategic Map [of the United States]. Twin Cities Sheet. Army Map Service, 1940. https://collections.library.yale.edu/catalog/15814589.

APA, 6th edition

of Engineers, U. S. A. C. (1940). Strategic map [of the United States]. Twin Cities sheet. [Maps]. Army Map Service, https://collections.library.yale.edu/catalog/15814589.