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To most people, a nautical chart looks like a map of the sea. It is more than that. A map is a reference for getting around on land; a chart is a working instrument for navigating water safely, and because of that role it carries a certain legal standing and authority that a road map never has.
A section of a NOAA nautical chart. Credit: NOAA.
What each one shows
A nautical chart presents hydrographic data — detailed information about the water. That includes water depths, the shoreline, tide predictions, obstructions such as rocks and shipwrecks, and aids to navigation.
A map emphasizes landforms, and the word covers a wide range of geographic and cartographic products: road maps, atlases and city plans are all maps. A map usually represents topographical information.
How each one is used
| Nautical chart | Map | |
|---|---|---|
| Used for | plotting courses, both across open water and through heavily trafficked areas | a reference showing set routes, such as roads and highways |
| Shows the hazards | yes — detailed information on hidden dangers to navigation | no — nothing about the condition of a road |
| Standing | a certain level of legal standing and authority | a reference guide |
Why the difference matters
A map tells you where the roads go; it says nothing about their condition. A chart's job is to show a mariner the dangers that are hidden — and because safe navigation depends on it, it is held to a different standard than a map.
Sources
Based on "What's the difference between a nautical chart and a map?" from NOAA's National Ocean Service, a work of the United States government in the public domain.
Licens: CC0 1.0 (allmän egendom) · Bearbetat efter oceanservice.noaa.gov
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