eli5, Why isn’t there a nautical kilometer?
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There sorta is, we just call it the kilometer.
Every five-year-old knows that a nautical mile is 1 minute of latitude, or 1/(360*60) of the circumference of the Earth.
When the metric system was laid out, the kilometer was deliberately sized to be 1/40000 of the circumference of the Earth, to be a nice round number.
Of course, the circumference of the Earth is different depending on which way around you go (equatorial circumference is not the same as polar circumference), and we’ve gotten more precise about measuring it since the kilometer was created, so we now base the kilometer on something that is more constant and more precisely known. So I just googled “circumference of Earth” and was told 40075 km. Not exact, but not bad.
The point is, the kilometer is sorta based on the size of the Earth, just like the nautical mile is.
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