What is a nautical mile?

A nautical mile is defined as the distance that corresponds to one minute of latitude as measured on the Earth's surface. This means that one nautical mile is equal to one-sixtieth of a degree of latitude. Since the Earth is spherical, a nautical mile is an essential measurement for navigation at sea and in the air. It allows mariners and pilots to relate distance directly to geographic coordinates, making it particularly useful when charting a course or determining position over the globe.

In contrast, the other options do not accurately define a nautical mile. The metric system, for example, uses meters and kilometers but does not typically utilize nautical miles, while saying it's equal to one mile is misleading, as a nautical mile is longer than a standard land mile—specifically, it's approximately 1.15078 statute miles. Moreover, it is not an exclusive measure for aviation, as nautical miles are also used in maritime navigation.