Grid Reference

Grid references define locations on maps using Cartesian coordinates. Grid lines on maps define the coordinate system, and are numbered to provide a unique reference to features.

Grid systems vary, but the most common is a square grid with grid lines numbered sequentially from the origin at the bottom left of the map. The grid numbers on the east-west (horizontal) axis are called Eastings, and the grid numbers on the north-south (vertical) axis are called Northings.

Numerical grid references consist of an even number of digits. Eastings are written before Northings. Thus in a 6 digit grid reference 123456, the Easting component is 123 and the Northing component is 456.

Grids may be arbitrary, or can be based on specific distances, for example the United Kingdom Ordnance Survey maps use a one-kilometre square grid spacing.

A grid reference locates a unique square region on the map. The precision of location varies, for example a simple town plan may use a simple grid system with single letters for Eastings and single numbers for Northings. A grid reference in this system, such as 'H3', locates a particular square rather than a single point.

Points can be located by grid references on maps that use a standard system for Eastings and Northings, such as the Ordnance Survey National Grid used by the Ordnance Survey, and located by someone else using grid references, even if using maps of a different scale.

For Ordnance Survey maps, each Easting and Northing grid line is given a two-digit code, based on the British national grid reference system with origin point just off the southwest coast of the United Kingdom. Since the Eastings and Northings are one kilometre apart, a combination of a Northing and an Easting will give a four-digit grid reference describing a one-kilometre square on the ground. In the example map below, the town Little Plumpton lies in the square 6901, even though the writing which labels the town is in 6802 and 6902, most of the buildings (the orange boxed symbols) are in square 6901.

The more digits added to a grid reference, the more precise the reference becomes. To locate a specific building in Little Plumpton, a further two digits are added to the four-digit reference to create a six-digit reference. The extra two digits describe a position within the 1-kilometre square. Imagine (or draw or superimpose a Romer) a further 10x10 grid within the current grid square. Any of the 100 squares in the superimposed 10 x 10 grid can be accurately described using a digit from 0-9 (with 0 0 being the bottom left square and 9 9 being the top right square). for the church in Little Plumpton this gives the digits 6 and 7 (6 on the left to right axis (Eastings) and 7 on the bottom to top axis (Northings). These are added to the four-figure grid reference after the two digits describing the same coordinate axis, and thus our six-figure grid reference for the church becomes 696017. This reference describes a 100-metre by 100-metre square, and not a single point, but this precision is usually sufficient for navigation purposes. The symbols on the map are not precise in any case, for example the church in the example above would be approximately 100x200 metres if the symbol was to scale, so in fact the middle of the black square represents the map position of the real church, completely independent of the actual size of the church,

Grid references comprising larger numbers for greater precision could be determined using large-scale maps and an accurate Romer. This might be used in surveying but is not generally used for land navigating for walkers or cyclists etc. The growing availability and decreasing cost of handheld GPS receivers enables determination of accurate grid references without needing a map, but it is important to know how many digits the GPS displays to avoid reading off just the first six digits. A GPS unit commonly gives a ten-digit grid reference, based on two groups of five numbers for the Eastings and Northing values. Each successive increase in accuracy (from 6 digit to 8 digit to 10 digit) pinpoints the location by a factor of 10. Since, in the UK at least, a 6-figure grid reference identifies a square of 100-metre sides, an 8-figure reference would identify a 10-metre square, and a 10-digit reference a 1-metre square. In order to give a standard 6-figure grid reference from a 10-figure GPS readout, the 4th, 5th, 9th and 10th digits must be omitted so it is important not to read just the first 6 digits.

Other articles related to "grid reference, grid":

A151 Road - Description - Bourne
... Jurassic clay, it meets the A6121, a road designation which ends here, having begun at Morcott, grid reference SK926004 in Rutland, on the other side of the A1, hence its beginning with ... At grid reference TF118207, the road turns due eastwards at Friar Bar, where to judge by its name, at one stage was a toll bar ... comparatively grand establishments called Halls, Neslam Hall at grid reference TF1732, for example ...
Saddleworth - Geography - Settlements
... collection of villages and hamlets, including Settlement Population OS Grid reference Image Austerlands c. 2,000 grid reference SD984080 Denshaw c. 500 grid reference SD974106 Diggle c ...
Snow Patches In Scotland - The Cairngorms
... next, but the location where more survivals have been noted than any other is grid reference NH994010, close to the Garbh Uisge Beag, which drains into Loch Avon ... It sits at an altitude of 1,095 metres (3,593 ft) and is located at approximately grid reference NJ011046 ... metres (3,740 ft), these patches are located around grid reference NN940980 the two most long-lasting patches are known as "the Pinnacles" and "the Sphinx" after the rock ...
Blennerhasset And Torpenhow
... It includes the villages of Blennerhasset grid reference NY178415 and Torpenhow at NY202397 and the smaller settlement of Kirkland Guards at NY187401 ... A Roman Fort is situated on the old Roman Road between Old Carlisle grid reference NY263466 and Papcastle grid reference NY109314 ...
Wye (rail) - Examples By Region - Europe
... Its OS National Grid location is grid reference ST316887 ... railway station on Anglesey in Wales still retains its triangle, grid reference SH294789 which is occasionally used for turning charter trains or diesel hauled Pendolino electric sets ... Its location was grid reference SK914349 and it is shown on the 1963 edition of OS 1 inch to 1 mile sheet 113 ...

Famous quotes containing the word reference:

    I think, for the rest of my life, I shall refrain from looking up things. It is the most ravenous time-snatcher I know. You pull one book from the shelf, which carries a hint or a reference that sends you posthaste to another book, and that to successive others. It is incredible, the number of books you hopefully open and disappointedly close, only to take down another with the same result.
    Carolyn Wells (1862–1942)