MLA

Service, United States. Army Map. Boulogne [Cartographic Material] : City Plan / Prepared under the Direction of the Chief of Engineers, U.S. Army. Army Map Service, 1943. https://collections.library.yale.edu/catalog/15484346.

APA, 6th edition

Service, U. S. A. M. (1943). Boulogne [cartographic material] : city plan / prepared under the direction of the Chief of Engineers, U.S. Army. [Maps]. Army Map Service, https://collections.library.yale.edu/catalog/15484346.