What is a Nautical Mile?

A nautical mile isn't just an arbitrary distance; it's based on the Earth itself.

Degrees and Minutes

One nautical mile was historically defined as one minute of latitude along any meridian. Since the Earth is a sphere (mostly), this made navigation using charts and sextants much easier.

Knots

Speed at sea is measured in 'knots', which is one nautical mile per hour. The term comes from the old practice of throwing a log tied to a knotted rope overboard to measure speed.