Coordinate reference systems

OS Select+Build

The GeoPackage and CSV formats accessible via OS Select+Build are available in three different coordinate reference systems dependent on your selection:

• British National Grid (BNG: EPSG: 27700)

• British National Grid + ODN Height (EPSG: 7405)

• European Terrestrial Reference System (ETRS89: EPSG: 4258)

Default coordinate reference systems for OS Select+Build

The following table outlines the default coordinate reference system used by each OS NGD collection in OS Select+Build:

Collection	Default coordinate reference system
GB Address	British National Grid (EPSG: 27700).
Islands Address	European Terrestrial Reference System (EPSG: 4258)
Boundaries	British National Grid (EPSG: 27700).
Building Features	British National Grid (EPSG: 27700).
Named Features	British National Grid (EPSG: 27700).
Land Features	British National Grid (EPSG: 27700).
Land Use Features	British National Grid (EPSG: 27700).
Structure Features	British National Grid (EPSG: 27700).
Routing and Asset Management Information (RAMI)	British National Grid (EPSG: 27700) for all feature types, except the Average And Indicative Speed Feature Type which is British National Grid + ODN Height (EPSG: 7405).
Transport Features	British National Grid (EPSG: 27700).
Transport Network	British National Grid + ODN Height (EPSG: 7405) for most feature types in the collection; British National Grid (EPSG: 27700) for the Ferry Terminal, Path, Road, Road Junction, Street and Pavement Link Feature Types.
Water Features	British National Grid (EPSG: 27700).
Water Network	British National Grid + ODN Height (EPSG: 7405) for the Water Link and Water Node Feature Types; British National Grid (EPSG: 27700) for the Water Link Set Feature Type.

Selecting a coordinate reference system

When creating a new data package in OS Select+Build (the Download service for OS NGD), you can choose what coordinate reference system you'd like to receive the data in.

If you don't choose a particular coordinate reference system for your data package, OS Select+Build will automatically select the default coordinate reference systems for the feature types in your data package for you.

OS NGD APIs

OS NGD API – Features

The GeoJSON format accessible via OS NGD API – Features is available in four different coordinate reference systems:

• British National Grid (BNG: EPSG: 27700).

• World Geodetic System (WGS84: EPSG: 4326)

• British National Grid + ODN Height (EPSG: 7405)

• Web Mercator (EPSG: 3857)

OS NGD API – Tiles

The vector tiles format accessible via OS NGD API – Tiles is available in two different coordinate reference systems:

• British National Grid (BNG: EPSG: 27700)

• Web Mercator (EPSG: 3857)

Definitions for the coordinate reference systems available in the OS NGD

Coordinate reference system	Definition
British National Grid (BNG: EPSG: 27700)	The British National Grid (BNG) spatial reference system uses the OSGB36 geodetic datum and a single Modified Transverse Mercator projection for the whole of Great Britain. Positions on this projection are described using easting and northing coordinates in units of metres. The BNG is a horizontal spatial reference system only; it does not include a vertical (height) reference system.
British National Grid + ODN Height (EPSG: 7405)	The BNG with ODN height reference uses the OSGB36 geodetic datum and a modified Transverse Mercator projection for the whole of Great Britain. Positions in this system are described by easting and northing coordinates plus a height value, all in units of metres. Please note, this will only be available for some OS NGD feature types.
European Terrestrial Reference System (ETRS89: EPSG: 4258)	The European Terrestrial Reference System uses the ETRS89 geodetic reference system which is the EU-recommended frame of reference for European data. Positions on this projection are described using latitude and longitude, and coordinates are provided in degrees. ETRS89 is a horizontal spatial reference system only; it does not specify a vertical (height) reference system. Please note, this coordinate system is only used for the OS NGD Islands Address Collection due to the coverage of this data being Northern Ireland, Isle of Man, and the Channel Islands.
World Geodetic System (WGS84: EPSG: 4326)	The WGS84 spatial reference system uses the WGS84 geodetic datum. Positions on this projection are described as latitude and longitude, and coordinates are provided in decimal degrees. There will also be an option to receive this reference system via CRS 84, meaning the coordinates will be provided as longitude / latitude rather than latitude / longitude.
Web Mercator (EPSG: 3857)	Web Mercator is not a recognised geodetic system, but it is used for many visualisation and web mapping use cases. It uses the WGS84 geodetic datum, and positions on this projection are described as easting and northing, all in units of metres.