MLA

Section, Great Britain. War Office. General Staff. Geographical. German East Africa. Tanga. Sheet B. O.S.O., 1915. https://collections.library.yale.edu/catalog/15532754.

APA, 6th edition

Section, G. B. W. O. G. S. G. (1915). German East Africa. Tanga. Sheet B. [Maps]. O.S.O., https://collections.library.yale.edu/catalog/15532754.