Terrain and Height

These are features that denote the ground level at any given point. OS MasterMap Topography Layer does not contain height contours, instead it contains height information point features of known height.

Triangulation stations

These are physical marks that represent points in the national triangulation scheme. The best-known form is the triangulation pillar, often found on hill or mountain tops. Other forms include triangulation points placed on church towers and flagpoles. The coordinates of a triangulation station in the data are not usually the very accurate coordinates for the control point. The accurate coordinates of the control point can be obtained from Ordnance Survey (see sub-section below on spot height). All triangulation stations are shown, except for buried and surface blocks.

Spot height

These are non-physical points, the altitude of which (relative to Ordnance Datum) has been determined by levelling. All current spot heights are shown by a point feature or symbol. The altitude to one decimal place of a metre is shown by a textual description. The latest information on Ordnance Survey’s GPS, triangulation and control points can be found on the Triangulation Stations page of the OS website.

Bench marks are represented in OS MasterMap Topography Layer as a symbol to mark their position. The values for these bench marks are available from the Bench Mark Locator page of the OS website. It should be noted that the bench mark information is historic, and Ordnance Survey cannot guarantee its accuracy.