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The nautical mile, a unit of measurement used for air and sea travel, is based on the Earth’s circumference.

The Earth’s circumference can be broken down to 360 degrees, while each degree is divided into 60 minutes. The distance between minutes is equivalent to one nautical mile.

In the metric system, a nautical mile is equivalent to 1.852 kilometers. Thus, under the UN Convention of the Law of the Seas, a country’s so-called exclusive economic zone extends to about 200 nautical miles into the sea from its coast, a distance of 370.4 km in the metric system.

The nautical mile is not to be confused with the statute mile, which is equal to 1.6 kilometers.

Sources: Howstuffworks.com, Unitconversion.org,
Geography.about.com