Ordnance Survey National Grid

The Ordnance Survey National Grid reference system is a system of geographic grid references used in Great Britain, different from using Latitude and Longitude.

The Ordnance Survey (OS) devised the national grid reference system, and it is heavily used in their survey data, and in maps (whether published by the Ordnance Survey or commercial map producers) based on those surveys. Grid references are also commonly quoted in other publications and data sources, such as guide books or government planning documents.

A number of different systems exist that can provide grid references for locations within the British Isles: this article describes the system created solely for Great Britain and its outlying islands (including the Isle of Man); the Irish grid reference system is a similar system created by the Ordnance Survey of Ireland for the island of Ireland. The Universal Transverse Mercator coordinate system (UTM) is used to provide grid references for world-wide locations and this is the system commonly used for the Channel Islands. European-wide agencies also use UTM when mapping locations, or may use the military grid reference system (MGRS) system, or variants thereof.