A nautical chart is the single most important document aboard any vessel. Unlike a road map, which shows highways and intersections, a nautical chart reveals what lies beneath the water's surface, where the hazards are, and how to get safely from one point to another across open water.
Every commercial vessel, yacht, and government craft depends on accurate, corrected charts for safe passage planning and regulatory compliance.
What Is a Nautical Chart?
A nautical chart is a graphic representation of a navigable waterway and its adjacent coastline, specifically designed for marine navigation. Nautical charts depict water depths (soundings), the shape of the seafloor (bathymetry), shoreline configuration, locations of rocks, wrecks, shoals, and other hazards, positions and characteristics of aids to navigation (buoys, beacons, lights), anchorage areas, traffic separation schemes, magnetic variation, tidal information, and restricted zones.
A nautical chart differs from a standard geographic map in one critical respect: a chart focuses on what is underwater and what affects safe vessel movement, while a map focuses on what is above ground. Charts carry a certain level of legal authority. SOLAS and national regulations require vessels to carry charts for the waters in which they operate, and port state control inspectors verify chart coverage and correction status during inspections.
Nautical charts are constructed using the Mercator projection, which represents lines of constant compass bearing (rhumb lines) as straight lines on the chart. The Mercator projection makes course plotting straightforward, which is why it has remained the standard for maritime navigation since the 16th century.
What Information Does a Nautical Chart Show?
A well-produced nautical chart packs dense navigational information into a single sheet. Depth soundings are printed across the chart face, measured in meters, feet, or fathoms depending on the producing authority. Depth contour lines connect points of equal depth, showing the shape of the seabed. Charted depths reference a vertical datum, typically the lowest astronomical tide (LAT), so actual water depth is almost always equal to or greater than what appears on the chart.
Navigation aids appear as standardized symbols: circles for buoys, star patterns for lights, diamonds for beacons. The compass rose shows true north and magnetic north with current variation noted in the center. The title block provides the chart number, scale, projection, datum, and sounding units. For a detailed walkthrough of interpreting these elements, the ANS guide on how to read nautical charts covers each component step by step.
Types of Nautical Charts by Scale
Nautical charts are classified by scale, and the scale determines how much area the chart covers and how much detail it provides.
- Planning or ocean charts (scales of 1:1,000,000 and smaller) cover vast ocean areas with minimal coastal detail. Navigators use these charts for plotting transoceanic passages and monitoring overall voyage progress.
- Sailing or general charts (scales from about 1:200,000 to 1:600,000) cover offshore waters and are used for coastwise navigation when the vessel is well clear of land and hazards.
- Coastal charts (scales from about 1:50,000 to 1:150,000) provide more detail for approaching land, entering major waterways, and transiting along the coast. Most day-to-day navigation aboard commercial vessels takes place on coastal charts.
- Harbor and approach charts (scales of 1:50,000 and larger) offer the greatest detail. Port approaches, narrow channels, anchorages, and berthing areas require these large-scale charts. Missing a required harbor chart during a port approach is one of the most common deficiencies found during port state control inspections.
A complete chart folio matched to the vessel's trading pattern is a SOLAS requirement. The ANS paper chart folio catalogue helps navigators and fleet managers verify coverage across all required scales for any intended voyage.
Who Produces Nautical Charts?
Official nautical charts are produced by national hydrographic offices. The United Kingdom Hydrographic Office (UKHO) publishes the ADMIRALTY chart series, with over 3,500 charts covering global commercial shipping routes. ADMIRALTY charts are the most widely used series for international trading vessels, accepted by port state control authorities in nearly every jurisdiction.
The National Oceanic and Atmospheric Administration (NOAA) produces charts covering all U.S. coastal waters, harbors, the Intracoastal Waterway, and the Great Lakes. Other major hydrographic offices include the Canadian Hydrographic Service (CHS), the French Service Hydrographique et Océanographique de la Marine (SHOM), and the Secretaría de Marina (SEMAR) of Mexico. American Nautical Services is an authorized distributor for UKHO, NOAA, CHS, SHOM, SEMAR, and other hydrographic offices, providing nautical charts corrected to the latest Notices to Mariners.
The International Hydrographic Organization (IHO) coordinates chart production standards worldwide and oversees the development of the INT chart series, which aims to unify national chart systems into a single international standard.
Paper Charts vs. Electronic Navigational Charts
Nautical charts are available in two formats: paper charts and electronic navigational charts (ENCs). Paper charts are printed on large sheets and used with traditional plotting tools such as parallel rulers, dividers, and pencils. ENCs are digital chart databases displayed on an Electronic Chart Display and Information System (ECDIS).
A type-approved ECDIS, such as the SEALL ECDIS, integrates ENC data with real-time GPS position, radar overlay, and AIS targets. Route monitoring, anti-grounding alarms, and automatic chart correction are built into the system. ECDIS has become the primary navigation method aboard most commercial vessels.
SOLAS Chapter V, Regulation 19 requires vessels to carry adequate, up-to-date nautical charts for the intended voyage. Vessels with a type-approved ECDIS and adequate backup may be exempt from a full paper folio, though many operators maintain paper charts as a secondary system.
SOLAS Requirements for Nautical Charts
SOLAS Chapter V, Regulation 19.2.1.4 requires all vessels to carry "nautical charts and nautical publications to plan and display the ship's route for the intended voyage and to plot and monitor positions throughout the voyage." Regulation 27 further requires that charts and publications be adequate and up to date.
Carrying outdated or uncorrected charts does not satisfy the carriage requirement. A chart that has not been corrected for the latest Notices to Mariners is effectively non-compliant. Port state control officers check chart folios against the vessel's planned voyage and verify that corrections are current. Maintaining updated SOLAS publications and charts aboard is a baseline compliance obligation for every commercial vessel.
How Nautical Charts Are Kept Up to Date
The marine environment changes constantly. New wrecks, shifted sand bars, relocated buoys, and newly surveyed depths all require chart corrections. Hydrographic offices publish weekly Notices to Mariners (NTMs) detailing every correction that must be applied.
For paper charts, corrections are applied by hand using NTM information. For ENCs, corrections are distributed digitally and applied automatically through services like ADMIRALTY Vector Chart Service (AVCS). A chart is only as safe as its last correction. Regularly ordering new editions, applying weekly NTMs without delay, and verifying folio coverage are essential practices for every navigation officer.
Get the Right Charts for Every Voyage
Safe navigation starts with the right chart at the right scale, corrected to the latest information. Whether building a new paper folio, transitioning to ECDIS, or verifying chart coverage for an upcoming voyage, American Nautical Services provides charts from UKHO, NOAA, CHS, SHOM, and other hydrographic offices, all corrected to date. Contact ANS at +1 (954) 522-3321 or sales@amnautical.com.
Frequently Asked Questions
Q. What is the difference between a nautical chart and a map?
A nautical chart is designed for marine navigation and focuses on water depths, underwater hazards, aids to navigation, and coastline features. A map focuses on land features such as roads, terrain, and buildings. Charts carry legal authority under SOLAS and national maritime regulations.
Q. What are the main types of nautical charts?
Nautical charts are classified by scale: planning/ocean charts for transoceanic passages, sailing charts for offshore navigation, coastal charts for near-shore transit, and harbor/approach charts for port entry and berthing. Larger-scale charts show more detail over smaller geographic areas.
Q. Are paper nautical charts still required on ships?
SOLAS requires all vessels to carry adequate, up-to-date nautical charts. Vessels with type-approved ECDIS and adequate backup may be exempt from a full paper folio, but many operators maintain paper charts as a secondary navigation system.
Q. Who makes official nautical charts?
National hydrographic offices produce official charts. Major producers include the UKHO (ADMIRALTY charts), NOAA (U.S. charts), CHS (Canadian charts), and SHOM (French charts). The IHO coordinates international charting standards.
Q. How often should nautical charts be corrected?
Charts should be corrected weekly using Notices to Mariners published by the relevant hydrographic office. New editions should be obtained when published. A chart that has not been corrected to the latest NTM is considered non-compliant during port state control inspections.
Q. What is an ENC?
An Electronic Navigational Chart (ENC) is a digital chart database designed for display on an ECDIS. ENCs contain the same navigational data as paper charts but allow automated position monitoring, route checking, and digital correction updates.
