AIS: Automatic Identification System. A system for identifying, locating, and communicating between vessels by integrating an electronic navigation system with a GPS and a VHF transceiver system.

ARPA: Automatic Radar Plotting Aid. A radar that is ARPA-enabled can create tracks using radar contacts—calculating the tracked object's course, speed, and closest point of approach (CPA)—in order to warn of a potential collision.

ASCII: American Standard Code for Information Interchange. A simple computer format for representing alphanumeric information such as waypoint and route names, and latitude and longitude.

Bathymetric: The data of water depth, creating a representation of the topography of the sea bottom.

BSB: A digital file format for raster charts co-developed by Maptech and NOAA. It is now the standard format for North American raster chart files.

BSB4, BSB5: Proprietary versions of BSB files that require registration through Maptech. Only a limited number of vendors support this format.

Coast Pilots: A nine-volume annual government publication that supplements U.S. nautical charts with information such as channel descriptions, anchorages, bridge and cable clearances, currents, tide and water levels, prominent features, dangers, routes, traffic separation schemes, small-craft facilities, and federal regulations.

Copy (versus "Load"): To move a computer file from one location to another. Files can by copied between folders, drives, or external media such as CDs or DVDs.

CPA: Closest Point of Approach. The calculated minimum distance between two objects. It is used for tracking and collision avoidance.

CRADA: Cooperative Research and Development Agreement. An agreement between a private company and a government agency to work together on a project in order to speed the commercialization of a federally-developed technology.

DNCs: Digital Nautical Charts. The National Geospatial-Intelligence Agency's trademarked name for its vector-format chart data files. An alternative vector format to ENCs.

Dongle: A small hardware device, also called a hardware key, which connects to a computer to authenticate the software application and prevent illegal copying.

DSC: Digital Selective Calling. A device that has DSC capability is able to "dial" and "ring" other DSC-equipped radios, including instantly sending an automatically formatted distress call.

ECS: Electronic Charting System. A system of hardware devices integrating a personal computer or dedicated chartplotter device with chart data files and additional vessel marine electronic devices.

ENCs: Electronic Navigational Charts. NOAA's trademark name for its vector-format chart data files.

GEO/NOS: A digital file format for raster charts used by SoftChart, now largely superceded by Maptech's BSB format.

Georeferencing: The process of scaling, rotating, translating and de-skewing an image to match a size and position using a common reference system such as latitude and longitude. It is necessary to establish a match between raster and vector images, and to combine and layer data from different sources.

GPS: Global Positioning System. A receiver that uses a constellation of satellites that transmit microwave signals to determine the receiver's location, speed, and direction.

GPX: GPS Exchange Format. An interchange format to transfer GPS data such as waypoints and routes.

GRIB: Gridded Binary. A data format used in meteorology to store historical and forecasted weather data.

Heading Sensor: A gyro compass/electromagnetic device that measures a vessel's heading, pitch and roll (attitude), and rate of turn.

HO: Hydrographic Office. The government organization responsible for conducting marine surveys and publishing nautical charts of that country's coastal waters.

IENC: Inland Electronic Navigation Charts. Vector-format digital charts of the U.S. Inland Waterway System, created by the U.S. Army Corps of Engineers.

Load (versus "Copy"): To tell a software application where particular files are located. Chart data files are loaded either by copying files to a designated folder ("smart folder" loading) or by pointing the application to the set of chart files ("directory" loading).

MARPA: Mini Automatic Radar Plotting Aid. A radar that is MARPA-equipped monitors a selected target to provide Closest Point of Approach (CPA) and Time to Closest Point of Approach (TCPA) data. It is used to avoid collisions.

NDI Digital Ocean Charts: Canadian charts in raster and vector formats.

NMEA 0183: An industry standard for electrical and data specifications, set by the National Marine Electronics Association (NMEA), for communication between marine electronic devices.

NOAA: National Oceanic and Atmospheric Administration. The federal agency responsible for oceanic and atmospheric data that includes the NOS and the Office of Coast Survey.

NOS: National Ocean Service. An agency within NOAA that includes the Office of Coast Survey.

Office of Coast Survey: The hydrographic office (HO) of the United States, responsible for producing and maintaining the nautical charts of the coastal waters of the U.S. and its territories.

Polar Diagram: A diagram showing a vessel's speed at different angles of sail in different wind strengths, used to determine target speed for any given wind speed and direction.

Radar: Originally an acronym for Radio Detection and Ranging. It is a system that transmits radio waves—reflected by a target and detected by the receiver—to collect information on the target's range, altitude, direction, or speed.

Raster (versus "Vector"): A digital chart in raster format is a scanned image of a paper chart. The data file is comprised of millions of picture elements, or pixels, representing the original image color and tone.

RNCs: Raster Navigational Charts. NOAA's trademark name for its raster-format chart data files.

Route: A collection of waypoints, connected in sequence, typically marking a vessel's intended course.

Sirius: A satellite radio company. Commercial-free subscription radio, news, and weather is received via Internet or a Sirius radio device.

S-57: An international format for vector digital charts, developed by the International Hydrographic Organization (IHO).

TCPA: Time to Closest Point of Approach. The calculated time until the minimum distance between two objects. Used for tracking and collision avoidance.

Track: A recording of the vessel's path.

USACE: U.S. Army Corps of Engineers. The federal agency responsible for surveying and charting the U.S. Inland Waterway System.

Vector (versus "Raster"): A digital chart in vector format is created from a database file of chart features and attributes. The data file consists of a collection of geospatially reference points, lines, polygons, symbols, and areas —and their associated attributes.

WAAS: Wide Area Augmentation System. A feature on GPS receivers to improve position accuracy, typically to within three meters, using a system of approximately 25 ground reference stations positioned across the U.S. that monitor satellite data.

Waypoint: A set of latitude and longitude coordinates that identify a location used for navigation.

XM: A subscription satellite radio service that includes XM WX Weather and XM Satellite Radio.