A nautical chart is a graphic representation of a maritime area and adjacent coastal regions. The National Oceanic and Atmospheric Administration ( NOAA) is a scientific agency within the United States Department of Commerce focused on the conditions of the Puerto Rico (ˌpwertoˈriko officially the Commonwealth of Puerto Rico ("Estado Libre Asociado de Puerto Rico" {{lang-en|"Associated Free State of Puerto Rico"}} This article is about the body of water For other uses see SEA and Seas. The coast is defined as the part of the land adjoining or near the Ocean. 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. The scale of a Map is the ratio of a single unit of distance on the map to the equivalent distance on the ground Water is a common Chemical substance that is essential for the survival of all known forms of Life. A topographic map is a type of Map characterized by large-scale detail and quantitative representation of relief, usually using Contour lines in modern Navigation is the process of reading and controlling the movement of a craft or vehicle from one place to another Characteristics A tide is a repeated cycle of sea level changes in the following stages Over several hours the water rises or advances up a beach in the flood A current, in a River or Stream, is the Flow of Water influenced by Gravity as the water moves Downhill to reduce its Earth 's magnetic field (and the surface magnetic field) is approximately a Magnetic dipole, with one pole near the North pole (see A harbor or harbour (see spelling differences) or haven, is a place where ships may shelter from the Weather or are stored A bridge is a Structure built to span a Gorge, Valley, Road, railroad track, River, Body of water 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. 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
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Sources and publication of nautical charts
Nautical charts are based on hydrographic surveys. Hydrographic survey in its strictest sense is the process of gathering information about navigable waters for the purposes of safe navigation of vessels 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. A sounding line or lead line is a length of thin Rope with a Plummet, generally of Lead, at its end In modern times, echo sounding is used for measuring the seabed in the open sea. Echo sounding is the technique of using Sound pulses directed from the surface or from a submarine vertically down to measure the distance to the bottom by means of sound waves 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. A shipwreck can refer to a wrecked ship or to the event that caused the wreck such as the striking of something that causes the ship to sink the stranding of the ship on rocks A wire is a single usually cylindrical, elongated string of drawn Metal. This ensures that difficult to find projections, such as masts, do not present a danger to vessels navigating over the obstruction. The mast of a sailing ship is a tall vertical or near vertical Spar, or arrangement of Spars which supports the Sails Large ships have several masts
Nautical charts are issued by the national hydrographic offices in many countries. A hydrographic office is an organization which is devoted to acquiring and publishing hydrographic information 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. A hydrographic office is an organization which is devoted to acquiring and publishing hydrographic information 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. The International Hydrographic Organization (IHO was originally established in 1921 as the International Hydrographic Bureau (IHB
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, Summary of Corrections, and Broadcast Notice to Mariners. Summary of Corrections A close companion to the Notice to Mariners is the Summary of Corrections. United States In the United States notices are issued by each U Summary of Corrections A close companion to the Notice to Mariners is the Summary of Corrections. 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.
Map projection, positions, and bearings
The Mercator projection is almost universally used in nautical charts. The Mercator projection is a cylindrical map projection presented by the Flemish geographer and cartographer Gerardus Mercator, in 1569 There are however some exceptions for very large or small scales where projections such as the gnomonic projection may be used. The concept of scale is applicable if a system is represented proportionally by another system The gnomonic Map projection displays all Great circles as straight lines 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. In Mathematics, a conformal map is a function which preserves Angles In the most common case the function is between domains in the Complex plane
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. Longitude (ˈlɒndʒɪˌtjuːd or ˈlɒŋgɪˌtjuːd symbolized by the Greek character Lambda (λ is the east-west Geographic coordinate measurement Latitude, usually denoted symbolically by the Greek letter phi ( Φ) gives the location of a place on Earth (or other planetary body north or south of the Geodetic systems or geodetic data are used in Geodesy, Navigation, Surveying by Cartographers and Satellite navigation systems The World Geodetic System defines a reference frame for the earth for use in Geodesy and Navigation.
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. This is about the direction for other uses see North (disambiguation. In Navigation, a course is the intended path of a vehicle over the surface of the Earth On nautical charts, the top of the chart is always true north, rather than magnetic north, towards which a magnetic compass points. noted by the Chinese Polymath Shen Kuo in the 11th century and possibly the egyptians over 6 millenia ago The 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 A compass, magnetic compass or mariner's compass is a navigational instrument for determining direction relative to the earth's Magnetic poles It consists Most charts include a compass rose depicting the variation between magnetic and true north. For Compass Airlines an Airline in the US using the Callsign "Compass Rose" See Compass Airlines A compass rose is a figure displaying the orientation The 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
Electronic and paper charts
Conventional nautical charts are printed on large sheets of paper at a variety of scales. The Bering Strait (Берингов пролив Beringov proliv) is a sea Strait between Cape Dezhnev, Russia, the easternmost point (169°43' The scale of a Map is the ratio of a single unit of distance on the map to the equivalent distance on the ground 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. 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
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. Automatic label placement (sometimes called text placement or name placement) refers to the computer methods of placing labels automatically on a map or chart
Details on a nautical chart
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, seamarks and landmarks. 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 A sea mark, also seamark and Navigation mark, is a Pilotage aid which identifies the approximate position of a maritime channel hazard Some symbols describe the sea bed with information such as its depth, depth contours, materials as well as possible hazards such as shipwrecks. A shipwreck can refer to a wrecked ship or to the event that caused the wreck such as the striking of something that causes the ship to sink the stranding of the ship on rocks Other symbols show the position and characteristics of buoys, lights, lighthouses, coastal and land features and structures that may be useful for position fixing. See also Lighthouse Pilotage Isophase light Flashing light Occulting light A lighthouse is a Tower, building or framework designed to emit light from a system of lamps and lenses or in older times from a fire and used as an Position fixing is the branch of Navigation concerned with the use of a variety of visual and electronic methods to determine the position of a Ship,
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. Underwater is a term describing the realm below the surface of Water where the water exists in a natural feature (called a body of water) such as an Ocean
Depths
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. The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International Older charts, as well as those published by the United States government, may use feet or fathoms. A foot (plural feet or foot; symbol or abbreviation ft or sometimes &prime – the prime symbol) is a non-SI unit A fathom is a unit of Length in the Imperial system (and the derived U Depth contour lines show the underwater topography. A contour line (also Level set, isopleth, isoline, isogram or isarithm) of a function of two Topography ( topo-, "place" and graphia, "writing" is the study of Earth 's Surface features or those of Planets Coloured areas of the sea emphasise shallow water and dangerous underwater obstructions. Depths are measured from the chart datum, which will be stated on the chart; this is often the depth of the lowest tide caused by gravity alone which is known as the "Lowest Astronimical Tide". The chart datum is the level of water that charted depths displayed on Nautical charts are measured from Gravitation is a natural Phenomenon by which objects with Mass attract one another
Tidal information
Tidal races and other strong currents have special chart symbols. Tidal race (or tidal rapid) is a natural occurrence whereby a fast moving Tide passes through a constriction resulting in the formation of Waves eddies 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. Tidal diamonds are symbols on British Admiralty charts that indicate the direction and speed of tidal streams.
See also
- Aeronautical chart
- Automatic label placement
- Nautical publications
- American Practical Navigator
- Coast Pilots
- Light List
- List of Lights
- Local Notice to Mariners
- Notice to Mariners
- Sailing Directions
- World Port Index
- Distances Between Ports
- Admiralty chart
External links
- Online version of Chart No.1 with "Symbols, Abbreviations and Terms" used in nautical charts
- Nautical Charts - chapter from the online edition of Nathaniel Bowditch's American Practical Navigator
- Sample Chart A sample chart of New York Harbor
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