The British National Grid, also known as the Ordnance Survey National Grid reference system (OSGB36), is a system of geographic grid references used in Great Britain. It is distinct from latitude and longitude.
The system was devised by the Ordnance Survey (OS) and is heavily used in its survey data, and in maps based on those surveys, whether published by the Ordnance Survey or by commercial map producers. Grid references are also commonly quoted in other publications and data sources, such as guide books and government planning documents.
The British National Grid transforms OSGB36 coordinates to Eastings and Northings, using a Transverse Mercator projection with a central meridian of -2 degrees, a false origin of 400 km west and 100 km north of the true origin, and a scale factor of 0.9996012717 at the central meridian.