This is an A3 same size copy of the Ordnance Survey Map of 1865 covering Salisbury Plain.
Note re Copyright:
Under the Copyright, Designs and Patents Act 1988, ‘Crown’ copyright exists for a period of 50 years from the end of the year in which the work was first published. This means that any OS mapping which was created prior to 1 April 2015 will be protected by Crown copyright for a period of 50 years from its first publication. Accordingly, if an OS map was first published over 50 years ago it can be copied or otherwise used without a licence from OS.