A chart is not a map

A side scan sonar image of an unknown wreck taken by the NOS Office of Coast Survey. While underwater hazards are marked on nautical charts to aid mariners, a map of the land does not similarly show road conditions for overland travelers.

A nautical chart provides a very detailed and accurate representation of the coastline, which takes into account varying tidal levels and water forms, critical to a navigator.

A map, on the other hand, emphasizes land forms, with shoreline represented much less accurately.

A chart is continually updated and is used by navigators to plot courses. A map, on the other hand, is a static document which serves as a reference guide.

Nautical charts also provide detailed information on the area beneath the water surface, which is critical for safe and efficient navigation. Maps provide no information of the condition of a road.

For more information:
Office of Coast Survey
Nautical Charts: A Message in a Bottle, NOS Education