Ethnographical map [cartographic material].
MLA
Section, Great Britain. War Office. General Staff. Geographical. Ethnographical Map [Cartographic Material]. War Office, 1918. https://collections.library.yale.edu/catalog/15826906.
APA, 6th edition
Section, G. B. W. O. G. S. G. (1918). Ethnographical map [cartographic material]. [Annotations (Provenance)--20th century, Maps]. War Office, https://collections.library.yale.edu/catalog/15826906.