A nautical mile is a unit of length used in air, marine, and space navigation, and for the definition of territorial waters.

[13] An earlier manuscript map by Nicolaus Germanus in a previous edition of Geography states "unul gradul log.

"[15] By the late 16th century English geographers and navigators knew that the ratio of distances at sea to degrees was constant along any great circle (such as the equator, or any meridian), assuming that Earth was a sphere.

In 1574, William Bourne stated in A Regiment for the Sea the "rule to raise a degree" practised by navigators: "But as I take it, we in England should allowe 60 myles to one degrée: that is, after 3 miles to one of our Englishe leagues, wherefore 20 of oure English leagues shoulde answere to one degrée.

[20] Both Gunter and Oughtred put forward the notion of dividing a degree into 100 parts, but their proposal was generally ignored by navigators.

[22] France and other metric countries state that in principle a nautical mile is an arcminute of a meridian at a latitude of 45°, but that is a modern justification for a more mundane calculation that was developed a century earlier.

By the mid-19th century, France had defined a nautical mile via the original 1791 definition of the metre, one ten-millionth of a quarter meridian.

This is potentially useful for celestial navigation on a human mission to the planet, both as a shorthand and a quick way to roughly determine the location.