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Information about Nautical Chart

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A 1976 United States NOAA chart of part of Puerto Rico
A nautical chart is a graphic representation of a maritime area and adjacent coastal regions. Depending on the scale 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 man-made aids to navigation, information on tides and currents, local details of the Earth's magnetic field, and man-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 or computerised electronic navigational charts.

Locations and bearings

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 map 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 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 magnetic compass points. Most charts include a compass rose depicting the variation between magnetic and true north.

The Mercator projection is almost universally used in nautical charts. There are however some exceptions for very large or small scales where projections such as the gnomonic projection may be used. Since the Mercator projection is conformal, that is, bearings in the chart are identical to the corresponding angles in nature, bearings may be measured from the chart to be used at sea or plotted on the chart from measurements taken at sea.

Pilotage information on charts

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Detail of a United States NOAA chart, showing a harbour area
The chart uses symbols to provide pilotage information about the nature and position of features useful to navigators, such as sea bed information, seamarks and landmarks. Some symbols describe the sea bed with information such as its depth, depth contours, materials as well as possible hazards such as shipwrecks. Other symbols show the position and characteristics of buoys, lights, lighthouses, coastal and land features and structures that may be useful for position fixing.

Colour may be used to distinguish between man-made features, dry land, sea bed that dries with the tide and seabed that is permanently underwater and to indicate water depth.

Depths

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Use of colour in British Admiralty charts
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 fathoms. Depth contour lines show the underwater topography. Coloured areas of the sea emphasise shallow water and dangerous underwater obstructions.

Tidal information

Tidal races and other strong currents have special chart symbols. Tidal flow information may be shown on charts using tidal diamonds, indicating the speed and bearing of the tidal flow during each hour of the tidal cycle.

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 not always reliable. 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, 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 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.

Electronic and paper charts

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Portion of an electronic chart of the Bering Strait
Conventional nautical charts are printed on large sheets of paper at a variety of scales. 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 most mariners carry paper charts as a back up in case the electronic charting system fails.

Labeling nautical charts



Nautical charts must be labeled with navigational and depth information. There are a few software solutions in the market that do label placement automatically for any kind of map or chart. For more information visit the Wikipedia article on Automatic label placement.

Chart correction

The nature of a waterway depicted by a chart changes regularly, and a mariner navigating on an old or uncorrected chart is courting disaster. Every producer of nautical charts also provides a system to inform mariners of changes that effect 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, Summary of Corrections, and Broadcast Notice to Mariners. Radio broadcasts give advance notice of urgent corrections.

A convenient 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.

Various and diverse methods exist for the correction of electronic navigational charts.

See also

External links

The three-letter acronym SEA may refer to:
  • Scientists and Engineers for America, a pro-science political advocacy group.
  • Schoof-Elkies-Atkin algorithm
  • Seattle-Tacoma International Airport (IATA: SEA, ICAO: KSEA)
  • Sea Education Association

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coast is defined as the part of the land adjoining or near the ocean. A coastline is properly a line on a map indicating the disposition of a coast, but the word is often used to refer to the coast itself.
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The scale of a map is the ratio of a single unit of distance on the map to the equivalent distance on the ground. The scale can be expressed in four ways: as a ratio, a fraction, in words and as a graphical (bar) scale.
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Water is a common chemical substance that is essential to all known forms of life.[1] In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor.
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topographic map is a type of map characterized by large-scale detail and quantitative representation of relief, usually using contour lines in modern mapping, but historically using a variety of methods.
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Navigation is the process of planning, recording, and controlling the movement of a craft or vehicle from one place to another.[1] The word navigate is derived from the Latin roots navis meaning "ship" and agere meaning "to move" or "to direct.
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Tides are the cyclic rising and falling of Earth's ocean surface caused by the tidal forces of the Moon and the Sun acting on the oceans. More generally, tidal phenomena can occur in any object that is subjected to a gravitational field that varies in time and space, such as the
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A current, in a river or stream, is the flow of water influenced by gravity as the water moves downhill to reduce its potential energy. The current varies spatially as well as temporally within the stream, dependent upon the flow volume of water, stream gradient, and channel
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Earth's magnetic field (and the surface magnetic field) is approximately a magnetic dipole, with one pole near the north pole (see Magnetic North Pole) and the other near the geographic south pole (see Magnetic South Pole).
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harbor or harbour (see spelling differences), or haven, is a place where ships may shelter from the weather or are stored. Harbors can be man-made or natural. A man-made harbor will have sea walls or breakwaters and may require dredging.
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bridge is a structure built to span a gorge, valley, road, railroad track, river, body of water, or any other physical obstacle. Designs of bridges will vary depending on the function of the bridge and the nature of the terrain where the bridge is to be constructed.
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An electronic navigational chart (ENC) is an official database created by a national hydrographic office for use with an Electronic Chart Display and Information System (ECDIS).
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equator divides the planet into a Northern Hemisphere and a Southern Hemisphere, and has a latitude of 0. Longitude is the east-west geographic coordinate measurement most commonly utilized in cartography and global navigation.
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equator divides the planet into a Northern Hemisphere and a Southern Hemisphere, and has a latitude of 0. Latitude, usually denoted symbolically by the Greek letter phi, , gives the location of a place on Earth north or south of the equator.
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This article describes a concept from surveying and geodesy. Datum is also the singular form of data. For the Austrian magazine, see Datum.


Geodetic systems or geodetic data
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The World Geodetic System defines a reference frame for the earth, for use in geodesy and navigation. The latest revision is WGS 84 dating from 1984 (last revised in 2004), which will be valid up to about 2010.
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Not to be confused with Bering or Baring.


Bearing may refer to:
  • Bearing (navigation), a term for direction
  • Bearing (mechanical), a component that separates moving parts and takes a load

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North is one of the four cardinal directions, specifically the direction that, in Western culture, is treated as the primary direction: north is used (explicitly or implicitly) to define all other directions; the (visual) top edges of maps usually correspond to the
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Course, in navigation, is the intended flight path of an airplane over the ground; or the direction of a line drawn on a chart representing the intended airplane path, expressed as the angle measured from a specific reference datum clockwise from 0° through 360° to the line.
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True north is a navigational term referring to the direction of the North Pole relative to the navigator's position. Its concept was first discovered and noted by the Chinese polymath Shen Kuo in the 11th century.
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magnetic declination (also known as grid magnetic angle in military circles) at any point on the Earth is the angle between the local magnetic field -- the direction the north end of a compass points -- and true north.
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For other uses, see Compass (disambiguation).


COMPASS is an acronym for COMPrehensive ASSembler. COMPASS is a macro assembly language on Control Data Corporation's 3000 series, and on the 60-bit CDC 6000 series, 7600 and
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compass rose is a figure displaying the orientation of the cardinal directions, north, south, east and west on a map or nautical chart. Today the use and idea of a compass rose is found on or featured in almost all navigation systems, including nautical charts, NDB and VOR systems,
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magnetic declination (also known as grid magnetic angle in military circles) at any point on the Earth is the angle between the local magnetic field -- the direction the north end of a compass points -- and true north.
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The Mercator projection is a cylindrical map projection presented by the Flemish geographer and cartographer Gerardus Mercator, in 1569. It became the standard map projection for nautical purposes because of its ability to represent lines of constant true bearing or true
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The concept of scale is applicable if a system is represented proportionally by another system. For example, for a scale model of an object, the ratio of corresponding lengths is a dimensionless scale, e.g. 1:25; this scale is larger than 1:50.
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The gnomonic map projection displays all great circles as straight lines.

Thus the shortest route between two locations in reality corresponds to that on the map.
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conformal map is a function which preserves angles.

More formally, a map

w = f(z)


is called conformal (or angle-preserving) at z0
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Pilotage is the use of fixed visual references on the ground or sea by means of sight or radar to guide oneself to a destination, sometimes with the help of a map or nautical chart. People use pilotage for activities such as guiding vessels and aircraft, hiking and Scuba diving.
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sea mark, also seamark and navigation mark, is a pilotage aid which identifies the approximate position of a maritime channel, hazard and administrative area to allow boats, ships and seaplanes to navigate safely.
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