Some may know this and some may "knot," but here goes nuttin'.
Having been boating on the Pacific Ocean for 30 years and having had my own boat for 20 years I have learned a thing or two. A nautical mile "by definition" is 1 minute of latitude. When you are out on the ocean the only way you know where you are is to know what your latitude and longitude is. Everyone on the ocean has their GPS set to nautical miles/knots. With that knowledge you can go to a chart and find your location.
So if the earth is 360° in circumference, and there are 60 minutes in each degree, the earth is 360x60=21,600 minutes around, or "by definition" 21,600 nautical miles around. Now the countries of the world just have to agree on what the statute miles in circumference the earth is and you have your ratio of statute (road) miles to nautical miles. A knot of speed refers to 1 nautical mile per hour and is what Wild and Free said:
1.150779448023543 mph
Here comes the wrinkle. Lines of latitude are parallel, so a minute of latitude (north/south) is always 1 nautical mile anywhere on the globe. BUT since lines of longitude are widest at the equator and meet at the poles, a minute of longitude (east/west) varies as you move north or south from the equator. Where I go out in the Pacific crabbing off of Half Moon Bay (36° north latitude) a minute of longitude is only about 0.85% of a nautical mile. It requires some thinking if you are moving from one location to another to meet someone.
Steve.
