MLA

Section, Great Britain. War Office. General Staff. Geographical. Congo Belge. Geographical Section, General Staff, 1921. https://collections.library.yale.edu/catalog/15533525.

APA, 6th edition

Section, G. B. W. O. G. S. G. (1921). Congo Belge. [Maps]. Geographical Section, General Staff, https://collections.library.yale.edu/catalog/15533525.