Cite

Great Britain Ordnance Survey edition of 1920.

MLA

Great Britain Ordnance Survey Edition of 1920. Ordnance Survey Office, 1920. https://collections.library.yale.edu/catalog/15826795.

APA, 6th edition

Great Britain Ordnance Survey edition of 1920. (1920). [Maps]. Ordnance Survey Office, https://collections.library.yale.edu/catalog/15826795.