Home > British national grid reference system
This article is about the map grid references in the UK. For the electric power transmission system in the UK, see National Grid.The British national grid reference system is a system of geographic grid references commonly used in Great Britain.
1 Usage
In general, neither the United Kingdom nor Ireland use latitude or longitude in describing internal geographic locations. Instead grid reference systems are in common usage. There are two such systems and this article describes the one used for Great Britain and its outlying islands; the system used throughout Ireland (including Northern Ireland) is the Irish national grid reference system.
The national grid referencing system was devised by the Ordnance Survey, and is heavily used in their survey data, and in maps (whether published by the Ordnance Survey or commercial map producers) based on those surveys. Additionally grid references are commonly quoted in other publications and data sources, such as guide books or government planning documents.
2 Grid Letters
The area of Great Britain is divided into a number of squares, identified by a pair of letters, measuring 100km by 100km. In practice many of these squares cover only sea; the ones which contain land are indicated on the adjoining map.
3 Eastings and Northings
Within each square, eastings and northings from the origin (south west corner) of the square are given numerically. For example, HL0305 means 'square HL, 3 km east, 5 km north'. A location can be indicated to varying resolutions numerically, usually from two digits in each coordinate (for a 1 km square) through to five (for a 1 m square); the most common usage is the six figure grid reference, employing three digits in each coordinate to determine a 100 m square. For example, the grid reference of the 100m square containing Ben Nevis, at (216683, 771279), is NN166712. Note that conversion to lower precision is through truncation, not rounding.
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