Title: Grid reference system - Wikipedia
Headings: Grid reference system
Grid reference system
Contents
Grid coordinates
Notation and conventions
Grid north
Types
See also
References

Content: Other conventions can also be used, such as a truncated grid reference, which would shorten the example coordinates to 949-361 . Negative northing and easting values indicate a position due south and west of the origin, respectively. Usually associated with a map projection is a natural origin, e.g., at which the ellipsoid and flat map surfaces coincide. 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. Grid north
Grid north ( GN) is a navigational term referring to the direction northwards along the grid lines of a map projection. It is contrasted with true north (the direction of the North Pole) and magnetic north (the direction in which a compass needle points). 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. 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. The grid lines point to a Grid North, varying slightly from True North. 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.