Nautical chart
Graphic representation of sea regions essential for safe navigation.
A nautical chart, also known as a hydrographic chart, is a graphic representation of a sea region or water body and adjacent coasts or banks. It is an essential tool for marine navigation, showing depths of water (bathymetry) and heights of land (topography), natural features of the seabed, coastline details, navigational hazards, natural and human-made aids to navigation, information on tides and currents, local details of the Earth's magnetic field, and human-made structures such as harbours, buildings, and bridges. Many countries require vessels, especially commercial ships, to carry them. Nautical charts may be printed on paper (raster navigational charts) or exist as computerized electronic navigational charts. Modern technology allows paper charts to be printed "on demand" using cartographic data downloaded to the printing company as recently as the night before printing, with critical updates like Local Notices to Mariners added daily to ensure the chart is current at the time of printing.
Charts are based on hydrographic and bathymetric surveys, which are laborious and time-consuming, meaning data for many areas may be dated and unreliable. Depths are measured historically with a sounding line and, in modern times, with echo sounding. To verify safe depth over obstructions like shipwrecks, the minimum depth is checked by sweeping the area with a horizontal wire. All depths are measured relative to a datum or reference level to ensure that difficult-to-find projections, such as masts, do not endanger vessels. National hydrographic offices issue official charts, often with regular manual updates through sales agents. The International Hydrographic Organization coordinates the international chart series ("INT" chart series) to unify chart systems worldwide. Commercially published charts also exist, sometimes offering additional information for specific users like yacht skippers.
Because waterways and aids to navigation can change rapidly, old or uncorrected charts must never be used. Producers provide systems like Notices to Mariners, Local Notices to Mariners, and Broadcast Notices to Mariners to inform mariners of changes. A Chart and Publication Correction Record Card system helps navigators track corrections, applying them only when a chart is needed. Digital systems like Digitrace, Voyager, or ChartCo can correct British Admiralty and NOAA charts
- field
- Hydrography and marine navigation
- known_for
- Essential tool for marine navigation; shows bathymetry, topography, hazards, and aids to navigation
- types
- Paper (raster navigational charts) and electronic navigational charts
- data sources
- Hydrographic surveys and bathymetric surveys
- publication authorities
- National hydrographic offices; also commercially published
- projection
- Primarily Mercator projection; also gnomonic and polyconic
Lore & Background
Nautical charts are based on hydrographic and bathymetric surveys, which are laborious and time-consuming, so data for many areas may be dated or unreliable. Historically, depths were measured with a sounding line; modern methods include echo sounding and sweeping with a horizontal wire to check minimum depth over obstructions. All depths are measured relative to a datum or reference level to ensure safety. Charts are issued by national hydrographic offices and are considered 'official,' as opposed to commercial publishers' charts. The International Hydrographic Organization coordinates an international chart series (INT) to unify chart systems worldwide. Chart corrections are provided via systems such as Notice to Mariners, Local Notice to Mariners, and Broadcast Notice to Mariners; print-on-demand charts can include corrections downloaded as recently as the night before printing. As stated in the Mariners Handbook, 'No chart is infallible. Every chart is liable to be incomplete.'
Reader's Guide
Nautical charts are foundational to maritime safety, providing mariners with critical information for route planning and hazard avoidance. Their significance is underscored by legal requirements in many countries for commercial vessels to carry them. The development of electronic navigational charts and print-on-demand paper charts has improved timeliness of corrections, but the inherent limitations of survey data mean uncharted dangers remain a risk, as demonstrated by several notable groundings and collisions. The Mercator projection, used on most nautical charts, allows direct use of plotted courses as steering bearings, though it distorts distances at high latitudes. The international coordination through the International Hydrographic Organization aims to standardize charting worldwide, but national hydrographic offices remain the primary authorities. The legacy of nautical charts is their role in enabling global maritime commerce and exploration, while their limitations remind users that no chart is infallible and that continuous correction and prudent seamanship are essential.
Did You Know?
- Nautical charts may be printed on paper (raster navigational charts) or as computerized electronic navigational charts.
- Depths on charts are measured relative to a datum or reference level to ensure safe clearance over obstructions like masts.
- The Mercator projection is used on the vast majority of nautical charts because it is conformal, allowing bearings to be used directly as course-to-steer.
Frequently Asked Questions
What is a Nautical chart?
A Nautical chart is a specialized map of a sea area, its coastline, and the seabed beneath it, designed specifically to help mariners plot safe passages. It is sometimes called a hydrographic chart and serves as the fundamental reference for anyone navigating open water.
What information does a Nautical chart display?
It layers together water depths, land elevations, seabed composition, shoreline details, known hazards, and man-made structures like buoys and lighthouses. It also includes tidal data, current patterns, and magnetic variation so a navigator can account for environmental shifts.
What types of Nautical charts exist?
There are two main formats: traditional paper charts (raster navigational charts) printed on durable material, and Electronic Navigational Charts (ENCs) loaded onto onboard computer systems. Both are built from the same hydrographic and bathymetric survey data.
Who is responsible for producing Nautical charts?
National hydrographic offices in each country are the primary authorities that commission surveys and publish official charts for their waters. Commercial publishers also produce versions, but the government offices remain the canonical source.
Why is a Nautical chart considered important in the fan community?
It is the single most critical safety document a vessel can carry; many nations legally mandate that commercial ships keep current charts aboard at all times. Without it, a navigator would have no reliable way to avoid shoals, wrecks, or other dangers hidden beneath the surface.
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