MLA

Section, Great Britain. War Office. General Staff. Geographical. Boa Vista / Drawn at War Office, 1940, from a Portuguese Map of 1924. Army Map Service, U.S. Army, 1943. https://collections.library.yale.edu/catalog/15238415.

APA, 6th edition

Section, G. B. W. O. G. S. G. (1943). Boa Vista / drawn at War Office, 1940, from a Portuguese map of 1924. [Maps]. Army Map Service, U.S. Army, https://collections.library.yale.edu/catalog/15238415.