I was incorrect, it is a six-inch map, difficult to tell when zooming on the screen. The Irish series has a different specification to the Great Britain series which I am used to, those have 25ft. contours. The Irish ones are earlier, c1830-40, arising out of a decision to send most of the OS surveyors there to sort out land-rent problems by mapping the townlands. The one-inch scale was not large enough so the six-inch was developed for Ireland, then continues initially in northern England and central Scotland, before the 1:2500 was commenced c1858. These early engraved maps have a special soft quality which was lost when production moved over to lithography.
