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The equator is divided into 360 degrees of longitude, so each degree at the equator represents 111,319.5 metres (365,221 ft). As one moves away from the equator towards a pole, however, one degree of longitude is multiplied by the cosine of the latitude, decreasing the distance, approaching zero at the pole.
The British National Grid sets Northing at (latitude 49 degrees North, longitude 2 degrees West) to be -100,000 meters exactly. It uses the Airy spheroid, with equatorial radius being 6377563.39603 meters and the reciprocal of the flattening being 299.3249645938 (both values being rounded); the meridian distance from the equator to 49 degrees ...
Since one degree is 1 / 360 of a turn, or complete rotation, one arcminute is 1 / 21 600 of a turn. The nautical mile (nmi) was originally defined as the arc length of a minute of latitude on a spherical Earth, so the actual Earth's circumference is very near 21 600 nmi. A minute of arc is π / 10 800 of a radian.
Degrees, minutes and seconds, when used, must each be separated by a pipe ("|"). Map datum must be WGS84 if possible (except for off-Earth bodies). Avoid excessive precision (0.0001° is <11 m, 1″ is <31 m). Maintain consistency of decimal places or minutes/seconds between latitude and longitude. Latitude (N/S) must appear before longitude (E/W).
In the table below conversions from mrad to metric values are exact (e.g. 0.1 mrad equals exactly 1 cm at 100 meters), while conversions of minutes of arc to both metric and imperial values are approximate.
The micrometre (SI symbol: μm) is a unit of length in the metric system equal to 10 −6 metres ( 1 / 1 000 000 m = 0. 000 001 m). To help compare different orders of magnitude , this section lists some items with lengths between 10 −6 and 10 −5 m (between 1 and 10 micrometers , or μm).
where φ (°) = φ / 1° is φ expressed in degrees (and similarly for β (°)). On the ellipsoid the exact distance between parallels at φ 1 and φ 2 is m(φ 1) − m(φ 2). For WGS84 an approximate expression for the distance Δm between the two parallels at ±0.5° from the circle at latitude φ is given by
Each variant of the metric system has a degree of coherence—the derived units are directly related to the base units without the need for intermediate conversion factors. [18] For example, in a coherent system the units of force , energy , and power are chosen so that the equations