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What's the difference between a nautical chart and a map?

A chart is more than a map

 a NOAA Nautical Chart

Section of a NOAA Nautical Chart.

A nautical chart represents hydrographic data, providing very detailed information on water depths, shoreline, tide predictions, obstructions to navigation such as rocks and shipwrecks, and navigational aids.

The term “map,” on the other hand, emphasizes landforms and encompasses various geographic and cartographic products. Some examples of maps might be road maps or atlases, or city plans. A map usually represents topographical information.

A chart is used by mariners to plot courses through open bodies of water as well as in highly trafficked areas. Because of its critical importance in promoting safe navigation, the nautical chart has a certain level of legal standing and authority. A map, on the other hand, is a  reference guide showing predetermined routes like roads and highways.

Nautical charts provide detailed information on hidden dangers to navigation. Maps provide no information of the condition of a road.