Harley, J. B. Ordnance survey maps : a descriptive manual / J.B. Harley. - Southhampton, UK : Ordnance Survey, 1975. - xvi, 201 p. : ill. Bibliography: p. 185-191. Subjects--Corporate Names: Great Britain. Ordnance Survey. Subjects--Topical Terms: Cartography--Great Britain.Topographic maps.