A chart is more than a map

sonar image of unknown underwater wreck

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 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.

For more information:

Office of Coast Survey

Travel the Seas: An Animated Primer on Nautical Charts

Podcast: Historical Charts and Maps (Diving Deeper)

Nautical Charts: A Message in a Bottle, NOS Education