For the measurement of distances navigation uses nautical mile. Nautical Mile equals to 1852 meters and is sub- divided into cables of one tenth of the nautical mile. The maximum value of a mile at the poles is 1864 meters and the minimum value at the equator is 1842,8 meters.
In navigation the term ‘distance’ defines the length of the imaginary line that connects two points on the Earth’s surface.
In general, speed is the covered distance in the unit of time. When at sea, speed is measured in knots. The knot equals to a mile per hour speed.