# 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](https://www.ordnancesurvey.co.uk/gps/legacy-control-information/triangulation-stations). 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](https://www.ordnancesurvey.co.uk/benchmarks/). It should be noted that the bench mark information is historic, and Ordnance Survey cannot guarantee its accuracy. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.os.uk/os-downloads/products/maps-and-imagery-portfolio/os-mastermap-topography-layer/os-mastermap-topography-layer-technical-specification/product-themes/terrain-and-height.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.