Ordnance Survey of Great Britain 1/4 inch to one mile.Great Britain. Ordnance Survey1920-21.Altitudes given in feet.Contours at 200 feet vertical intervals.Copy 2: Includes sheets 1, 2A, 3, 4A, 6A, 7A, 9A (two copies), 10-11, and 12A, with various corrections between 1928 and 1930.Diagram showing adjoining sheets in margins.cartographic