any of a large series of high quality, detailed maps of Great Britain produced in a variety of scales originally for military, but now for leisure or business use
An Ordnance Survey map is a detailed map produced by the British or Irish government map-making organization. a map which shows all the roads, paths, hills etc of an area in detail (Because the maps were originally made for the department responsible for ordnance: ordnance (14-20 centuries), from ordenance)