What is the basic unit used for distance on nautical charts?

• A. Statute Mile (SM)
• B. Fathom
• C. Nautical Mile (NM)
• D. Kilometer

Answer: (C)

Distance on nautical charts is expressed in nautical miles. This unit fits how charts are laid out, since a nautical mile is defined as one minute of latitude along any meridian, which is exactly 1,852 meters (about 6,076 feet). Because degrees, minutes, and seconds organize positions on the chart, using nautical miles lets you measure distance directly in relation to those divisions and connect it to travel time and speed. Fathoms are a depth measure, not distance on a chart, and kilometers or statute miles are not the standard chart distance units. Ships typically use knots for speed, which matches distance in nautical miles per hour. Therefore the basic unit for distance on nautical charts is the nautical mile.