Distance

The measured separation between two positions or features.

Marine distances are commonly expressed in nautical miles, where one international nautical mile is exactly 1,852 metres. Shorter distances may use cables or metres, while chart scales and electronic systems can use different units according to context and settings.

A distance may be measured along a route, as a straight geodesic or rhumb-line separation, or as range from an observer. The method matters over long distances and around hazards; the shortest numerical distance is not necessarily the safe navigable distance.