Cite

Europe 1:2,000,000 : Berlin-Wien, M.N. 33. 34.

MLA

Survey, Great Britain. Ordnance. Europe 1:2,000,000 : Berlin-Wien, M.N. 33. 34. Ordnance Survey, 1919. https://collections.library.yale.edu/catalog/15238241.

APA, 6th edition

Survey, G. B. O. (1919). Europe 1:2,000,000 : Berlin-Wien, M.N. 33. 34. [Maps]. Ordnance Survey, https://collections.library.yale.edu/catalog/15238241.