Which unit is commonly used for large distances at sea?

The commonly used unit for large distances at sea is the nautical mile. A nautical mile is defined as one minute of latitude and is equivalent to approximately 1.15078 statute miles or 1.852 kilometers. This unit is particularly important in maritime navigation and is used in aviation as well, as it directly relates to the Earth's geometry.

The reason the nautical mile is utilized over other units for measuring distance at sea is due to its direct correlation to the global coordinate system. Navigators can easily calculate distance based on the latitude and longitude of their position, making the nautical mile especially relevant in navigation where angles and the curvature of the Earth are taken into account.

While the marine league is an older and less common historical measure used primarily in maritime contexts, the nautical mile has become the standardized unit for navigation over large distances. Other options, such as chain and rod, are much smaller units typically used in land surveying rather than for measuring large distances at sea.