Kilometer:
A kilometer is defined as 1/10,000th of the average distance on Earth between the Equator and either Pole. Therefore, there are 10,000 kilometers from the Equator to either Pole.

Nautical Mile:
A nautical mile is the length of an arc of a Great Circle that subtends an angle of one minute at the Earth’s center of curvature. Due to the Earth’s flattening at the poles, the radius of curvature increases, requiring a greater arc length to subtend one minute of angle.

• At the poles, a nautical mile is approximately 6,108 feet.
• At the equator, it measures about 6,046 feet.
• The average value used universally is 6,076 feet.

Circumference of the Earth:
The circumference of the Earth, expressed in nautical miles, is calculated using:
Departure = Change of Longitude (in minutes) × Cos Latitude

For the equator (Latitude = 0°):
Departure = 360 × 60 × Cos 0 = 21,600 NM.

Thus, the Earth’s circumference is approximately 21,600 nautical miles