For Great Britain, the technical details are as follows: Spheroid The National Grid is then a cartesian coordinate system calculated on the resulting flat surface.ĭifferent spheroids and projections are used in different countries and regions of the world. This spheroid is then transformed onto a flat surface using a mathematical transformation known as a projection. In summary, the process is that the irregular shape of the Earth is approximated by an ellipsoid or spheroid. The details of the construction of the National Grid from latitude and longitude is mathematically complex. Since Eastings and Northings are measured in metres, you will need to add zeros to make the Eastings and Northings of the correct magnitude: e.g. For example, square NS is 200km East and 600km North of the origin, which becomes 2 units East and 6 units North.Īdd the appropriate 100km reference to the beginning of the rest of the reference (remembering to omit the letters): e.g. Use the diagram below to calculate how many 100km units east and north the bottom left hand corner of your square is. Work out the numerical reference for the two letters: e.g. Split the reference into its East and North components: e.g. Remove the two letters at the beginning of the reference: e.g. To convert a National Grid Reference to Eastings and Northings: Convert Grid Reference to Eastings and Northings Notice that there is always an even number of digits - usually 2,4 or 6. The second half of the digits give the Northing, or distance North from the edge of the 100km square. The first half of the digits give the Easting, or distance East from the edge of the 100km square. In a National Grid reference, the letters identify a 100km square and the digits identify a location within that 100km square. When using the Digimap Gazetteer service, you may need to convert from standard National Grid references to Eastings and Northings. However, National Grid references are measured differently, using letters to represent the 100km reference, for example, NS123456. For example, Jedburgh is at NT6520 or 365000 East, 620000 North. The origin of the National Grid is 000000 (metres) East and 000000 (metres) North. If there is a quadrant name present, it indicates one quarter of the area indicated by the rest of the grid reference.Įastings and Northings are measured in hundreds of thousands of metres (100,000 metres). No digits? The Grid Reference applies to the complete 100km square.10 digits: the Easting and Northing are each in units of 1m.8 digits: the Easting and Northing are each in units of 10m.6 digits: the Easting and Northing are each in units of 100m. 4 digits: the Easting and Northing are each in units of 1km.2 digits: the Easting and Northing are each in units of 10km.The second half of the digits give the Northing, or distance North from the edge of the 100km square.The first half of the digits give the Easting, or distance East from the edge of the 100km square.The digits identify a location within a 100km square. The resulting 100km squares covering Great Britain are shown here. The letters are allocated in alphabetical order from left to right and top to bottom, and omitting the letter “I”.Įach 500km square is then divided into twenty five 100km squares, and these squares are then labelled using the same pattern of letters. Ordnance Survey’s products lie completely within four of these 500km squares: H, N, S and T. The first letter identifies a 500km square, from the diagram shown here. Two letters together identify a 100km square, and are derived as follows: 1 However, spaces are included here for legibility. These components are usually written without spaces. a quadrant name: “NW”, “NE”, “SW” or “SE”, standing for North West, North East, South West and South East.an even number of digits, optionally followed by.OS introduction to the British National Grid. These references are often used in conjunction with Ordnance Survey maps, and are used to give the names of individual Ordnance Survey data tiles. The position of any point in Great Britain can be described by its National Grid Reference.
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