Grid reference
Encyclopedia
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 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 point 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 labeling 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.
MAPS
Maps is the plural of map, a visual representation of an area.As an acronym, MAPS may refer to:* Mail Abuse Prevention System, an organisation that provides anti-spam support...
using Cartesian coordinates. Grid lines on maps define the coordinate system
Coordinate system
In geometry, a coordinate system is a system which uses one or more numbers, or coordinates, to uniquely determine the position of a point or other geometric element. The order of the coordinates is significant and they are sometimes identified by their position in an ordered tuple and sometimes by...
, 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 based on specific distances, for example the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
Ordnance Survey
Ordnance Survey
Ordnance Survey , an executive agency and non-ministerial government department of the Government of the United Kingdom, is the national mapping agency for Great Britain, producing maps of Great Britain , and one of the world's largest producers of maps.The name reflects its creation together with...
maps use a one-kilometre square grid spacing.
A grid reference locates a unique point 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
Ordnance Survey
Ordnance Survey , an executive agency and non-ministerial government department of the Government of the United Kingdom, is the national mapping agency for Great Britain, producing maps of Great Britain , and one of the world's largest producers of maps.The name reflects its creation together with...
, and located by someone else using grid references, even if using maps of a different scale.
For Ordnance Survey
Ordnance Survey
Ordnance Survey , an executive agency and non-ministerial government department of the Government of the United Kingdom, is the national mapping agency for Great Britain, producing maps of Great Britain , and one of the world's largest producers of maps.The name reflects its creation together with...
maps, each Easting and Northing grid line is given a two-digit code, based on the British national grid reference system
British national grid reference system
The Ordnance Survey National Grid reference system is a system of geographic grid references used in Great Britain, different from using latitude and longitude....
with origin point just off the southwest coast of the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
. 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 labeling 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
Romer
A Reference Card or "Romer" is a device for increasing the accuracy when reading a grid reference from a map. Made from transparent plastic, paper or other materials, they are also found on most baseplate compasses. Essentially, it is a specially marked-out ruler which matches the scale of the map...
) 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
Romer
A Reference Card or "Romer" is a device for increasing the accuracy when reading a grid reference from a map. Made from transparent plastic, paper or other materials, they are also found on most baseplate compasses. Essentially, it is a specially marked-out ruler which matches the scale of the map...
. This might be used in surveying
Surveying
See Also: Public Land Survey SystemSurveying or land surveying is the technique, profession, and science of accurately determining the terrestrial or three-dimensional position of points and the distances and angles between them...
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.