Nautical Chart and Land Map: Different Information for Different Routes

A nautical chart depicts hydrographic information: coastlines, water depths, hazards in the water, and navigation aids. A general map, by contrast, usually focuses on terrain, places, and routes on land.

What a nautical chart shows in addition

Typical information on a nautical chart includes depth figures, depth contours, channels, shoals, known obstructions, and buoys or other navigation aids. Depending on the chart, anchorages and other features relevant to shipping may also be shown. Symbols and abbreviations are part of the information system: U.S. Chart No. 1, published by NOAA and the U.S. National Geospatial-Intelligence Agency, explains them for both paper charts and electronic nautical charts, as well as how they are displayed on navigation systems.

Thus, the chart shows not only where the coast runs, but also the charted conditions on and beneath the water. The precise meaning of a symbol is given in the chart legend and depends on the chart system being used.

Why a land map is not enough

A road map helps you find land routes and places. But as a rule, it shows neither water depths nor underwater hazards or nautical symbols in a channel. A coastal road and a shipping route may be close to one another and still require different information. A land map answers questions such as how roads and places are positioned relative to each other; a nautical chart relates depths and navigation marks to the waterway.

A simple comparison

Land map: terrain, roads, places, and land use.
Nautical chart: coastline, charted depths, channels, obstructions, and navigation aids.

Nautical chart data is also updated and corrected. NOAA distinguishes safety-critical corrections—such as newly discovered rocks, wrecks, or shoals, and changes to the positions or characteristics of buoys, beacons, and lights—from routine updates. Critical corrections are issued as updates for electronic nautical charts; extensive changes may require a new edition. This is why the chart edition and supplementary official notices matter in actual use.

Both types of maps may show areas of land, but they answer different questions. NOAA’s U.S. Chart No. 1 explains nautical chart symbols and terminology.