Why are there two different definitions that are close but not exactly identical?
In: 1
A mile is distantly based on an old Roman unit, the Roman mile, which was 1000 paces. This was 5000 Roman feet, but England placed more importance on the furlong and so the statute mile in England was redefined in 1593 to be 8 furlongs, or 5280 feet. This gives us the modern day US survey mile.
A nautical mile was based on latitude to make life easier for sailors. 1 minute of latitude is 1 nautical mile. It just happens to be a very similar distance to the survey mile.
This is also where knots come from. 1 nmi/h is 1 knot.
A land mile was historically established as a specific number of smaller length measures (feet, yards etc.), and has been in existence since Ancient Rome.
A nautical mile was established as a 1/60th fraction of one degree of latitude, since its useful to be this way in navigation, and also because that’s how you measure distances at sea (and not by counting feet or yards).
The nautical mile is really useful for sea travel because it is the distance of one minute of latitude and nautical charts measure using latitude and longitude. If you were travelling straight south at 10kts, or 10 nautical miles per hour, then it would take six hours to travel one degree of latitude.
1 nautical mile = 1.1508 miles.
Ref: [https://oceanservice.noaa.gov/facts/nautical-mile-knot.html](https://oceanservice.noaa.gov/facts/nautical-mile-knot.html)
The “statute” mile has its origins in ancient Rome and was the thousand paces as measured by every other step, one thousand times the left foot comes down.
https://en.wikipedia.org/wiki/Mile#Roman
There used to be all sorts of units called mile before they were almost all replaced by the metric system.
They were all roughly similar length based on the idea of a thousand steps, but each version was different.
The mile as used in America and the nautical mile along with a few obscure others are the lone survivors of this family
The nautical mile and the unit of knots (and cable) that is based on it, actually has a similar definition as the meter originally had. They are both based on the circumference of the earth.
Just that the meter actually is based on dividing the distance between equator and pole into 10,000,000 parts, while the nautical mile is based on dividing the same distance into 90 degrees and each degree into 60 minutes. One minute of latitude is a nautical mile.
This is useful when you navigate with maps where there is a line ever minute of latitude and longitude.
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