Learn about Nautical Cartography

An art and science
Cartographers in NOAA ’ sulfur Office of Coast Survey, Marine Chart Division commit the art and skill of designing, compiling, updating, and distributing nautical charts. nautical charts are a special character of map specifically tailored to the needs of marine navigation. Charts show water depths and the depiction of shoreline, outstanding topographical features and landmarks, aids to navigation, and other navigational information. A nautical graph is a sour area on which the navigator plot courses, ascertains positions, and views the relationship of the ship to the surrounding area. It assists navigators in avoiding dangers and arriving safely at their destination. When a ship ground, collision, or early marine accident occurs, the nautical graph in use at the clock time is a critical legal criminal record used to assist in reconstructing the event and assigning liability .
NOAA cartographers use sophisticate software and techniques to produce charts to exacting specifications. many processes are act and are applied in an static, taxonomic manner. however, every graph and every musical composition of reservoir corporeal to be compiled onto a chart is a bite different. therefore, cartographers are besides often called upon to make judgments, based on their years of train and know, regarding which features to depict on a particular chart, how to portray them, and how any compilation may affect the portrayal and interpretation of other features on the chart .
NOAA nautical charts are produced in a variety show of digital formats, which may be downloaded free from the Coast Survey web site ; paper copies of nautical charts are available for purchase from NOAA certified chart agents.

Flattening the Earth

nautical charts ( as do all maps of any helping of the Earth ) diagrammatically depict the ball-shaped land on a flat surface. The “ flatten ” is accomplished by projecting the positions of Earth ’ randomness features onto a surface that can be flattened. For nautical charts, this is most normally done by mathematically projecting spherical positions onto a cylinder. The cylinder may then be “ unfurl ” into a apartment surface, resulting in a orthogonal map .
A Mercator map is created by projecting positions from a celestial sphere onto a cylindrical surface
The orthogonal Mercator projection was beginning presented by the Flemish geographer and cartographer Gerardus Mercator in 1569. Most nautical charts use the Mercator projection, because any straight production line drawn on a Mercator chart is besides a line of changeless path, besides called a rhumb line line or rhumb line. This makes determining the direction to steer a ship over a class plotted on the chart a straightforward job of measuring the angle directly from the erect acme lines on the chart .

The Ever Changing Marine Environment

Storms affect the configuration of barrier islands and other shorelines. River delta sediment silt up, changing coastlines and the depths of channels and harbors. Buoys and other physical and virtual aids to seafaring are installed or moved to increase navigation base hit in our ever changing waters. Channels and harbors are dredged ; piers, wharf and other port facilities are added or improved ; marinas are build up or reconfigured. Regulations for recommend routes, vessel dealings interval schemes, anchorages, and restricted areas are approved. Bridges over navigable rivers and channels are built, and pipelines and power or communication cables are laid below them. These are good some of the thousands of changes that must be updated on nautical charts per annum .
Coast Survey receives information about these changes from scores of reservoir data providers, which include other federal, state and local government agencies, national and external regulative organizations, private companies, professional organizations, and secret citizens. Every chart does not change every workweek, but every workweek Coast Survey releases updates to those that have.

A Chart Scale for Every Navigational Purpose

More detail ( larger scale ) charts are required when navigating close to shore ( where shoals and other dangers to navigation are more numerous, and within ports, where cognition of the location and characteristics of channels, buoys and other aids to navigation, piers and early port facilities is vital to safely navigating to and from a ship ’ s mooring. thus, nautical charts are created in several scales. NOAA nautical chart scales range from 1:2,500 to 1:10 million. Charts are often categorized into the following six groups by scale ( from largest to smallest scale ), Berthing, Harbor, Approach, Coastal, General, and Sailing Charts. These names besides hint at the chart scale ’ randomness intended purpose .

Generalization

New data is normally applied to the largest scale charts first. The depiction of geographic data is then generalized for depiction on successively smaller scale charts. This is necessary, because smaller scale charts show larger areas on the same amount of newspaper ( or pixels ) as larger scale charts. Cartographers use several techniques to accomplish this, such as :

• Selection / exclusion – fewer features are shown on smaller scale charts. Large scale charts often show every buoy associated with a navigational channel, but smaller scale charts may show only two at the channel entrance.
• Simplification – shorelines and other crenulated features must be smoothed to be depicted on smaller scale charts, otherwise the curves would cluster together to produce an indistinguishable blob. A marina’s individual slips may be shown on large scale charts, but only the outline of the dock on smaller scale charts.
• Combination – similar features are combined at smaller scales. The same marina might be represented by a single marina point symbol on even smaller scale charts.
• Offsetting features – while close-by land features, such as roads and railroads, may be offset from each other for clarity, features within water, such as rocks, buoys, or channels limits, are never offset from their true positions. Other generalization techniques are used to portray these features at smaller scales, such as combining the depiction of
  separate nearby rocks to show them as a single ledge.

The pair of images below show the area between San Francisco ’ s Golden Gate Bridge and Alcatraz Island on successively smaller scale charts. The prototype on the left shows the stallion extent of each chart. The image on the correct shows the increasingly generalized portrait of the same area on a ten-spot column inch wide section of each chart .
1:20,000 scale Chart 18650
1:40,000 plate Chart 18649

1:207,840 scale Chart 18640
1:1,444,000 scale Chart 18020
1:4,860,700 scale Chart 530

beginning : https://mindovermetal.org/en
Category : Maritime