Cite

Europe 1:2,000,000 : Bucuresti-Constantinople, K.I. 35. 36.

MLA

Survey, Great Britain. Ordnance. Europe 1:2,000,000 : Bucuresti-Constantinople, K.I. 35. 36. Ordnance Survey, 1919. https://collections.library.yale.edu/catalog/15238242.

APA, 6th edition

Survey, G. B. O. (1919). Europe 1:2,000,000 : Bucuresti-Constantinople, K.I. 35. 36. [Maps]. Ordnance Survey, https://collections.library.yale.edu/catalog/15238242.