MLA

Section, Great Britain. War Office. General Staff. Topographical. Sierra Leone : French Guinea / Compiled in the Topographical Section, General Staff. War Office, 1909. https://collections.library.yale.edu/catalog/15533573.

APA, 6th edition

Section, G. B. W. O. G. S. T. (1909). Sierra Leone : French Guinea / compiled in the Topographical Section, General Staff. [Maps]. War Office, https://collections.library.yale.edu/catalog/15533573.