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The length of one minute of arc along a meridian is equal to one NM (1 852 m) at approximately latitude:
  • A
  • B
    30°
  • C
    45°
  • D
    90°

Because the Earth is flattened at the Poles, the radius of curvature is increased and a greater arc is required to subtend an angle of one minute at the centre of curvature, hence a nautical mile is longer at the Poles, at about 1 862 m.

The amount of curvature is greatest at the Equator (the radius of curvature is decreased) and therefore the length of arc required to generate an angle of one minute at the centre of curvature is less. A nautical mile is shortest at the Equator and measures about 1 844 m.

The average value is 1 852 m, which would correspond to 1 minute of arc of a Meridian measured at a latitude of approximately 45°.

Some examples of distances:

Latitude

Distance
(1º of latitude)

90º

60.31 NM (North Pole)

75º

60.27 NM

60º

60.16 NM

45º

60.01 NM

30º

59.86 NM

15º

59.75 NM

59.71 NM (Equator)

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