![]() ![]() A grid reference in this system, such as 'H3', locates a particular square rather than a single point. The precision of location varies, for example a simple town plan view may use a simple alphanumeric grid system with single letters for Eastings and single numbers for Northings. Grids may be arbitrary, or can be based on specific distances, for example some maps use a one-kilometre square grid spacing.Ī grid reference locates a unique square region on the map. if the smallest unit is 100 metres, it refers to a point 12.3 km east and 45.6 km north from the origin. Thus in a 6 digit grid reference 123456, the Easting component is 123 and the Northing component is 456, i.e. Numerical grid references consist of an even number of digits. 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. Grid systems vary, but the most common is a square grid with grid lines intersecting each other at right angles and numbered sequentially from the origin at the bottom left of the map. Since the meridians converge at the poles, true east and west directions change rapidly in a condition similar to gimbal lock. The difference exists because the correspondence between a flat map and the round Earth is necessarily imperfect.Īt the South Pole, grid north conventionally points northwards along the Prime Meridian. The difference between grid north and true north is very small and can be ignored for most navigation purposes. This variation is zero on the central meridian (north-south line) of the map, which is at two degrees West of the Prime Meridian, and greatest at the map edges. The grid lines point to a Grid North, varying slightly from True North. ![]() The grid lines on Ordnance Survey maps divide the UK into one-kilometre squares, east of an imaginary zero point in the Atlantic Ocean, west of Cornwall. Many topographic maps, including those of the United States Geological Survey and Great Britain's Ordnance Survey, indicate the difference between grid north, true north, and magnetic north. It is contrasted with true north (the direction of the North Pole) and magnetic north (the direction in which a compass needle points). Grid north ( GN) is a navigational term referring to the direction northwards along the grid lines of a map projection. Otherwise, negative northing and easting values indicate a position south and west of the origin, respectively. To ensure that the northing and easting coordinates on a map are not negative, map projections may set up a false origin, specified in terms of false northing and false easting values, that offset the true origin. Usually associated with a map projection is a natural origin, e.g., at which the ellipsoid and flat map surfaces coincide. This permits users to shorten the example coordinates to 949-361 by concealing 11U 05nnn34 56nnn74. Because the (leading) most significant digits specify the part of the world and the (trailing) least significant digits provide a precision that is not needed in most circumstances, they may be redundant for trekking use. Subset conventions can also be used, such as a truncated grid reference, where the general location is already known to participants and may be assumed. The pair is usually represented conventionally with easting first, northing second.įor example, the peak of Mount Assiniboine (at 50★2′10″N 115☃9′03″W) in UTM Zone 11 is represented by 11U 0594934 5636174. Locations can be found using easting/northing (or x, y) pairs. The coordinates are most commonly associated with the Universal Transverse Mercator coordinate system (UTM), which has unique zones that cover the Earth to provide detailed referencing. However, other units (e.g., survey feet) are also used. When using common projections such as the transverse Mercator projection, these are distances projected on an imaginary surface similar to a bent sheet of paper, and are not the same as distances measured on the curved surface of the Earth.Įasting and northing coordinates are commonly measured in metres from the axes of some horizontal datum. ![]() Easting is the eastward-measured distance (or the x-coordinate) and northing is the northward-measured distance (or the y-coordinate). Įasting and northing are geographic Cartesian coordinates for a point. UTM zones on an equirectangular world map with irregular zones in red. ![]()
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