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Somewhat more formally, Bowditch defines variation as "the angle between the magnetic and geographic meridians at any place, expressed in degrees and minutes east or west to indicate the direction of magnetic north from true north. The angle between magnetic and grid meridians is called grid magnetic angle, grid variation, or grivation." [1]
Maps issued by the United Kingdom Ordnance Survey contain a diagram showing the difference between true north, grid north, and magnetic north at a point on the sheet; the edges of the map are likely to follow grid directions rather than true, and the map will thus be truly rectangular/square. [citation needed]
If the reference direction is north (either true north, magnetic north, or grid north), the bearing is termed an absolute bearing. In a contemporary land navigation context, true, magnetic, and grid bearings are always measured in this way, with true north, magnetic north, or grid north being 0° in a 360-degree system. [5]
This image shows magnetic declination, or the angle between magnetic and geographic north, according to the World Magnetic Model released in 2025. Red is magnetic north to the east of geographic ...
The difference between grid north and true north is very small and can be ignored for most navigation purposes. The difference exists because the correspondence between a flat map and the round Earth is necessarily imperfect. At the South Pole, grid north conventionally points northwards along the Prime Meridian. [9] Since the meridians ...
Like the North Magnetic Pole, the North Geomagnetic Pole attracts the north pole of a bar magnet and so is in a physical sense actually a magnetic south pole. It is the center of the 'open' magnetic field lines which connect to the interplanetary magnetic field and provide a direct route for the solar wind to reach the ionosphere.
The projection introduces a distortion so that grid north differs from true north; magnetic north is a natural feature that differs from both. As an example: at 52° 35' N 1° 10' E (approx 7 km west of Norwich, England) true north is 2° 33' west of grid north, and magnetic north is about 7° west of grid north.
In the past five years, the magnetic north pole has significantly slowed down to about 25km a year. The model assists in guiding a smartphone's compass tools. It also contributes to GPS systems ...