
A nautical chart is a graphic representation of a sea area and adjacent coastal regions. Depending on the
scale
Scale or scales may refer to:
Mathematics
* Scale (descriptive set theory), an object defined on a set of points
* Scale (ratio), the ratio of a linear dimension of a model to the corresponding dimension of the original
* Scale factor, a number ...
of the chart, it may show depths of water and heights of land (
topographic map), natural features of the seabed, details of the coastline, navigational hazards, locations of 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. Nautical charts are essential tools for marine navigation; many countries require vessels, especially commercial ships, to carry them. Nautical charting may take the form of charts printed on paper (raster navigational charts) or computerized
electronic navigational charts. Recent technologies have made available paper charts which are printed "on demand" with cartographic data that has been downloaded to the commercial printing company as recently as the night before printing. With each daily download, critical data such as
Local Notices to Mariners are added to the on-demand chart files so that these charts are up to date at the time of printing.
Sources and publication of nautical charts
Nautical charts are based on
hydrographic surveys. As surveying is laborious and time-consuming, hydrographic data for many areas of sea may be dated and are sometimes unreliable. Depths are measured in a variety of ways. Historically the
sounding line was used. In modern times,
echo sounding is used for measuring the seabed in the open sea. When measuring the safe depth of water over an entire obstruction, such as a
shipwreck
A shipwreck is the wreckage of a ship that is located either beached on land or sunken to the bottom of a body of water. Shipwrecking may be intentional or unintentional. Angela Croome reported in January 1999 that there were approximately ...
, the minimum depth is checked by sweeping the area with a length of horizontal
wire. This ensures that difficult to find projections, such as
masts, do not present a danger to vessels navigating over the obstruction.
Nautical charts are issued by power of the national
hydrographic offices in many countries. These charts are considered "official" in contrast to those made by commercial publishers. Many hydrographic offices provide regular, sometimes weekly, manual updates of their charts through their sales agents. Individual hydrographic offices produce national chart series and international chart series. Coordinated by the
International Hydrographic Organization, the international chart series is a worldwide system of charts ("INT" chart series), which is being developed with the goal of unifying as many chart systems as possible.
There are also commercially published charts, some of which may carry additional information of particular interest, e.g. for yacht skippers.
Chart correction
The nature of a waterway depicted by a chart may change, and artificial aids to navigation may be altered at short notice. Therefore, old or uncorrected charts should never be used for navigation. Every producer of nautical charts also provides a system to inform mariners of changes that affect the chart. In the United States, chart corrections and notifications of new editions are provided by various governmental agencies by way of
Notice to Mariners,
Local Notice to Mariners
A Local Notice to Mariners is an authoritative instruction issued by a designated official, typically the harbormaster.
United States
In the United States, notices are issued by each U.S. Coast Guard District to disseminate important information ...
,
Summary of Corrections, and
Broadcast Notice to Mariners. In the U.S., NOAA also has a printing partner who prints the "POD" (print on demand) NOAA charts, and they contain the very latest corrections and notifications at the time of printing. To give notice to mariners, radio broadcasts provide advance notice of urgent corrections.
A good way to keep track of corrections is with a ''Chart and Publication Correction Record Card'' system. Using this system, the navigator does not immediately update every chart in the portfolio when a new ''Notice to Mariners'' arrives, instead creating a card for every chart and noting the correction on this card. When the time comes to use the chart, he pulls the chart and chart's card, and makes the indicated corrections on the chart. This system ensures that every chart is properly corrected prior to use. A prudent mariner should obtain a new chart if he has not kept track of corrections and his chart is more than several months old.
Various Digital Notices to Mariners systems are available on the market such as Digitrace, Voyager, or ChartCo, to correct British
Admiralty chart
Admiralty charts are nautical charts issued by the United Kingdom Hydrographic Office (UKHO) and subject to Crown Copyright. Over 3,500 Standard Nautical Charts (SNCs) and 14,000 Electronic Navigational Charts (ENCs) are available with the Admira ...
s as well as NOAA charts. These systems provide only vessel relevant corrections via e-mail or web downloads, reducing the time needed to sort out corrections for each chart. Tracings to assist corrections are provided at the same time.
The
Canadian Coast Guard produces the Notice to Mariners publication which informs mariners of important navigational safety matters affecting Canadian Waters. This electronic publication is published on a monthly basis and can be downloaded from the Notices to Mariners (NOTMAR) Web site. The information in the Notice to Mariners is formatted to simplify the correction of paper charts and navigational publications.
Various and diverse methods exist for the correction of electronic navigational charts.
Limitations
In 1973 the cargo ship ''MV Muirfield'' (a merchant vessel named after
Muirfield,
Scotland) struck an unknown object in the
Indian Ocean in waters charted at a depth of greater than 5,000 metres (16,404 ft), resulting in extensive damage to her
keel. In 1983,
HMAS ''Moresby'', a
Royal Australian Navy survey ship
A survey vessel is any type of ship or boat that is used for underwater surveys, usually to collect data for mapping or planning underwater construction or mineral extraction. It is a type of research vessel, and may be designed for the purpo ...
, surveyed the area where ''Muirfield'' was damaged, and charted in detail a previously unsuspected hazard to navigation, the
Muirfield Seamount. The dramatic accidental discovery of the Muirfield Seamount is often cited as an example of limitations in the vertical
geodetic datum accuracy of some offshore areas as represented on nautical charts, especially on small-
scale
Scale or scales may refer to:
Mathematics
* Scale (descriptive set theory), an object defined on a set of points
* Scale (ratio), the ratio of a linear dimension of a model to the corresponding dimension of the original
* Scale factor, a number ...
charts.
A similar incident involving a passenger ship occurred in 1992 when the
Cunard liner ''
Queen Elizabeth 2
''Queen Elizabeth 2'' (''QE2'') is a retired British ocean liner converted into a floating hotel. Originally built for the Cunard Line, the ship, named as the second ship named ''Queen Elizabeth'', was operated by Cunard as both a transatlantic ...
'' struck a submerged rock off
Block Island
Block Island is an island in the U.S. state of Rhode Island located in Block Island Sound approximately south of the mainland and east of Montauk Point, Long Island, New York, named after Dutch explorer Adriaen Block. It is part of Washingt ...
in the
Atlantic Ocean. In November 1999, the
semi-submersible,
heavy-lift ship ''
Mighty Servant 2'' capsized and sank after hitting an uncharted single underwater isolated pinnacle of granite off Indonesia. Five crew members died and ''Mighty Servant 2'' was declared a total loss. More recently, in 2005 the submarine
USS ''San Francisco'' ran into an uncharted sea mount (sea mountain) about 560 kilometres (350 statute miles) south of Guam at a speed of , sustaining serious damage and killing one seaman. In September 2006 the
jack-up barge
A jackup rig or a self-elevating unit is a type of mobile platform that consists of a buoyant hull fitted with a number of movable legs, capable of raising its hull over the surface of the sea. The buoyant hull enables transportation of the unit a ...
''Octopus'' ran aground on an uncharted sea mount within the
Orkney Islands
Orkney (; sco, Orkney; on, Orkneyjar; nrn, Orknøjar), also known as the Orkney Islands, is an archipelago in the Northern Isles of Scotland, situated off the north coast of the island of Great Britain. Orkney is 10 miles (16 km) north ...
(United Kingdom) while being towed by the tug ''Harold''. £1M worth of damage was caused to the barge and delayed work on the installation of a tidal energy generator prototype. As stated in the Mariners Handbook and subsequent accident report: "No chart is infallible. Every chart is liable to be incomplete".
Map projection, positions, and bearings

Historically the first projection, invented by
Marinus of Tyre ca. AD 100 according to
Ptolemy, was what is now called
equirectangular projection
The equirectangular projection (also called the equidistant cylindrical projection or la carte parallélogrammatique projection), and which includes the special case of the plate carrée projection (also called the geographic projection, lat/lon ...
(historically called plane chart, ''plate carrée'', pt, carta plana quadrada). While it is very convenient for small seas like the Aegean, it's unsuitable for seas larger than Mediterranean or an open ocean, even though early explorers had to use it for want of a better.
The
Mercator projection
The Mercator projection () is a cylindrical map projection presented by Flemish geographer and cartographer Gerardus Mercator in 1569. It became the standard map projection for navigation because it is unique in representing north as up and sou ...
is now used on the vast majority of nautical charts. Since the Mercator projection is
conformal
Conformal may refer to:
* Conformal (software), in ASIC Software
* Conformal coating in electronics
* Conformal cooling channel, in injection or blow moulding
* Conformal field theory in physics, such as:
** Boundary conformal field theory ...
, that is, bearings in the chart are identical to the corresponding angles in nature, courses plotted on the chart may be used directly as the course-to-steer at the helm.
The
gnomonic projection
A gnomonic map projection is a map projection which displays all great circles as straight lines, resulting in any straight line segment on a gnomonic map showing a geodesic, the shortest route between the segment's two endpoints. This is achie ...
is used for charts intended for plotting of
great circle routes.
NOAA
The National Oceanic and Atmospheric Administration (abbreviated as NOAA ) is an United States scientific and regulatory agency within the United States Department of Commerce that forecasts weather, monitors oceanic and atmospheric conditio ...
uses the
polyconic projection
The American polyconic map projection is a map projection used for maps of the United States and regions of the United States beginning early in the 19th century. It belongs to the polyconic projection class, which consists of map projections who ...
for some of its charts of the
Great Lakes, at both large and small scales.
Positions of places shown on the chart can be measured from the
longitude and
latitude scales on the borders of the chart, relative to a
geodetic datum such as
WGS 84.
A
bearing is the angle between the line joining the two points of interest and the line from one of the points to the north, such as a ship's
course
Course may refer to:
Directions or navigation
* Course (navigation), the path of travel
* Course (orienteering), a series of control points visited by orienteers during a competition, marked with red/white flags in the terrain, and corresponding ...
or a compass reading to a landmark. On nautical charts, the top of the chart is always
true north, rather than
magnetic north, towards which a compass points. Most charts include a
compass rose depicting the
variation
Variation or Variations may refer to:
Science and mathematics
* Variation (astronomy), any perturbation of the mean motion or orbit of a planet or satellite, particularly of the moon
* Genetic variation, the difference in DNA among individual ...
between magnetic and true north.
However, the use of the Mercator projection has drawbacks. This projection shows the lines of longitude as parallel. On the real globe, the lines of longitude converge as they approach the north or south pole. This means that east–west distances are exaggerated at high latitudes. To keep the projection conformal, the projection increases the displayed distance between lines of latitude (north–south distances) in proportion; thus a square is shown as a square everywhere on the chart, but a square on the Arctic Circle appears much bigger than a square of the same size at the equator. In practical use, this is less of a problem than it sounds. One minute of latitude is, for practical purposes, a nautical mile. Distances in nautical miles can therefore be measured on the latitude gradations printed on the side of the chart.
Nautical charts
on sailingissues.com
Electronic and paper charts
Conventional nautical charts are printed on large sheets of paper at a variety of scale
Scale or scales may refer to:
Mathematics
* Scale (descriptive set theory), an object defined on a set of points
* Scale (ratio), the ratio of a linear dimension of a model to the corresponding dimension of the original
* Scale factor, a number ...
s. Mariners will generally carry many charts to provide sufficient detail for the areas they might need to visit. Electronic navigational charts, which use computer software and electronic databases to provide navigation information, can augment or in some cases replace paper charts, though many mariners carry paper charts as a backup in case the electronic charting system fails.
Labeling nautical charts
Nautical charts must be labeled with navigational and depth information. There are a few commercial software packages that do automatic label placement for any kind of map or chart. Modern systems render electronic charts consistent with th
IHO S-52 specification
Details on a nautical chart
Many countries' hydrographic agencies publish a "Chart 1", which explains all of the symbols, terms and abbreviations used on charts that they produce for both domestic and international use. Each country starts with the base symbology specified in IHO standard INT 1, and is then permitted to add its own supplemental symbologies to its domestic charts, which are also explained in its version of Chart 1. Ships are typically required to carry copies of Chart 1 with their paper charts.
Pilotage information
The chart uses symbols to provide pilotage information about the nature and position of features useful to navigators, such as sea bed information, sea mark, and landmarks. Some symbols describe the sea bed with information such as its depth, materials as well as possible hazards such as shipwreck
A shipwreck is the wreckage of a ship that is located either beached on land or sunken to the bottom of a body of water. Shipwrecking may be intentional or unintentional. Angela Croome reported in January 1999 that there were approximately ...
s. Other symbols show the position and characteristics of buoy
A buoy () is a floating device that can have many purposes. It can be anchored (stationary) or allowed to drift with ocean currents.
Types
Navigational buoys
* Race course marker buoys are used for buoy racing, the most prevalent form of yac ...
s, lights, lighthouse
A lighthouse is a tower, building, or other type of physical structure designed to emit light from a system of lamps and lenses and to serve as a beacon for navigational aid, for maritime pilots at sea or on inland waterways.
Lighthouses mar ...
s, coastal and land features and structures that are useful for position fixing. The abbreviation "ED" is commonly used to label geographic locations whose existence is doubtful.
Colours distinguish between man-made features, dry land, sea bed that dries with the tide, and seabed that is permanently underwater and indicate water depth.
Depths and heights
Depths which have been measured are indicated by the numbers shown on the chart. Depths on charts published in most parts of the world use metres. Older charts, as well as those published by the United States government, may use feet or fathom
A fathom is a unit of length in the imperial and the U.S. customary systems equal to , used especially for measuring the depth of water. The fathom is neither an International Standard (SI) unit, nor an internationally-accepted non-SI unit. Hi ...
s. Depth contour lines show the shape of underwater relief. Coloured areas of the sea emphasise shallow water and dangerous underwater obstructions. Depths are measured from the chart datum, which is related to the local sea level. The chart datum varies according to the standard used by each national Hydrographic Office. In general, the move is towards using lowest astronomical tide (LAT), the lowest tide predicted in the full tidal cycle, but in non-tidal areas and some tidal areas Mean Sea Level (MSL) is used.
Heights, e.g. a lighthouse, are generally given relative to mean high water spring (MHWS). Vertical clearances, e.g. below a bridge or cable, are given relative to highest astronomical tide
High may refer to:
Science and technology
* Height
* High (atmospheric), a high-pressure area
* High (computability), a quality of a Turing degree, in computability theory
* High (tectonics), in geology an area where relative tectonic uplift to ...
(HAT). The chart will indicate what datum is in use.
The use of HAT for heights and LAT for depths, means that the mariner can quickly look at the chart to ensure that they have sufficient clearance to pass any obstruction, though they may have to calculate height of tide to ensure their safety.
Tidal information
Tidal races and strong currents have special chart symbols. Tidal flow information may be shown on charts using tidal diamond
Tidal diamonds are symbols on British admiralty charts that indicate the direction and speed of tidal streams.
The symbols consist of a letter of the ISO basic Latin alphabet in a rhombus, printed in purple ink. On any particular chart each tid ...
s, indicating the speed and bearing of the tidal flow during each hour of the tidal cycle.
See also
* Aeronautical chart
* Automatic label placement
*Admiralty chart
Admiralty charts are nautical charts issued by the United Kingdom Hydrographic Office (UKHO) and subject to Crown Copyright. Over 3,500 Standard Nautical Charts (SNCs) and 14,000 Electronic Navigational Charts (ENCs) are available with the Admira ...
* Bathymetric chart
*European Atlas of the Seas
The European Atlas of the Seas is an easy-to-use and interactive web-based atlas on the coasts and seas within and around Europe and provides information on Europe's marine environment. It is freely accessible on the internet. The latest version o ...
* Nautical star
* Navigation room
* Portolan chart
*Dutch maritime cartography in the Age of Discovery
The history of cartography refers to the development and consequences of cartography, or mapmaking technology, throughout human history. Maps have been one of the most important human inventions for millennia, allowing humans to explain and navi ...
(First printed atlas of nautical charts, 1584)
Further reading
*
References
External links
The Medieval and Early Modern Nautical Chart: Birth, Evolution and Use
Lisbon-based ERC-funded academic project. They develop and maintain th
MEDEA-CHART Database
a sophisticated search engine and aggregator of early nautical charts data.
* [https://web.archive.org/web/20090223175546/http://www.lumenartis.net/index.php?main_page=product_info&cPath=68&products_id=183&language=en&zenid=3e6dc909566a0f8e3fd73aa98aa30530 Portolan Chart of Gabriel de Vallseca, 1439]
*
Nautical charts available online (Nautical Free)
Online Nautical Charts Viewer
{{DEFAULTSORT:Nautical Chart