> For the complete documentation index, see [llms.txt](https://docs.os.uk/os-downloads/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.os.uk/os-downloads/products/land-and-terrain-portfolio/os-terrain-5/os-terrain-5-overview.md).
# OS Terrain 5 Overview
OS Terrain is the name given to Ordnance Survey’s height products. The two products available, OS Terrain 5 and OS Terrain 50, provide detailed three-dimensional digital terrain models (DTMs) of Great Britain. A DTM primarily defines the ground surface, having removed all protruding features (such as buildings and trees) elevated above the bare earth. The main difference between the two products is their level of resolution:
* **OS Terrain 5** is a mid-resolution DTM, designed to be interoperable with our large-scale data.
* **OS Terrain 50** is a lower-resolution DTM product, designed for landscape visualisation and analysis over large areas. It is an OS OpenData product and, as such, it is free to view, download and use for commercial, educational, and personal purposes.
OS Terrain 5 is published as both grid and contour data, each in a variety of formats. Both data types are created from the same source data and are supplied as 5km-by-5km tiles.
* **OS Terrain 5 grid**: a grid of heighted points with regular 5m post spacing.
* **OS Terrain 5 contours**: a contour dataset of 5m interval standard contour polylines, which includes index contours at 25m intervals, mean high and low water boundaries and spot heights.
## Key features of the product
* The product is maintained by our integrated 3 to 5-year flying programme and is synchronised with our other product updates.
* There is specific modelling of significant features, particularly networks.
* **DTM grid data** is available in ASCII (American Standard Code for Information Interchange) grid and Geography Markup Language (GML) 3.2.1, using Open Geospatial Consortium (OGC) Simple Features Profile (level 0).
* **DTM contour data** is available in GML 3.2.1, and Esri shapefile.
* There is full coverage of Great Britain.
* It is designed to work with Ordnance Survey’s large-scale data.
* Supplied as grid and contours with spot heights.
* The product is updated quarterly.
* It is based on the INSPIRE elevation specification.
## Product applications
OS Terrain 5 provides an ideal base to enable the third dimension for other data within an appropriate geographical information system (GIS). The height data has been created from a source that is also used to update our large-scale data products.
OS Terrain 5 can be used in conjunction with various Ordnance Survey digital products for analytical, modelling, planning and visual purposes. These uses enable customers to undertake the following:
* Asset/site management
* Environmental analysis
* Line of sight planning
* Viewshed modelling
* Landscape visualisation and fly-through sequences
* Planning and development
* Signal propagation
* Wind farm location planning
* Flood risk assessment
* Foundation for 3D modelling
## Accuracy
OS Terrain 5 has been measured against with GPS points in a range of sample areas to provide a root mean square error (RMSE) value, being the average of the mean height points in each geographic area: urban and major communication routes, rural, and mountain and moorland.
* Urban and major communication routes 1.5m RMSE
* Rural 2.5m RMSE
* Mountain and moorland 2.5m RMSE
## INSPIRE compliance
OS Terrain 5 is designed to be INSPIRE-ready. Ordnance Survey is a leading member of the UK Location Programme, which is charged with delivering INSPIRE, a directive that applies to all member states and aims to enable more joined-up data across public bodies for environmental applications.
At the time of OS Terrain product development, the INSPIRE elevation specification had not been finalised. The data structures of OS Terrain products, and the details of the GML encoding, have been based on the draft INSPIRE specification. For more information about INSPIRE and UK Location, please view the [INSPIRE web pages](https://inspire.ec.europa.eu/data-specifications/2892).
## Index
* [Product supply](/os-downloads/products/land-and-terrain-portfolio/os-terrain-5/os-terrain-5-overview/product-supply.md)
* [Pre-requisites](/os-downloads/products/land-and-terrain-portfolio/os-terrain-50/os-terrain-50-overview/pre-requisites.md)
* [Data structure](/os-downloads/products/land-and-terrain-portfolio/os-terrain-50/os-terrain-50-overview/data-structure.md)
* [Source data](/os-downloads/products/land-and-terrain-portfolio/os-terrain-50/os-terrain-50-overview/source-data.md)
* [The National Grid](/os-downloads/products/land-and-terrain-portfolio/os-terrain-5/os-terrain-5-overview/the-national-grid.md)
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