Glossary Archive

This shape represents the Letter G (Flag Semaphore) and the Number 7 (Flag Semaphore).

International Morse Code sequence representing the letter G.

A weather model developed by the National Centers for Environmental Prediction (NCEP) that provides global weather forecasts by simulating the atmosphere using mathematical equations and data from various sources.  The Global Forecast System (GFS) is a numerical weather prediction model that is used to produce forecasts for weather conditions globally. Developed by the National Centers...

An internationally agreed-upon set of safety procedures, communication protocols, and equipment designed to ensure that ships at sea can send and receive distress signals and safety information. The Global Maritime Distress and Safety System (GMDSS) was established by the International Maritime Organization (IMO) to enhance maritime safety and facilitate the efficient coordination of search and...

A map of the UK indicating the 3 sea areas around the coast and the coast of nearby European countries. White pointers indicate Medium Frequency (MF) and Very High Frequency (VHF) coast radio stations. Red pointers indicate a Very High Frequency (VHF) coast radio station. Sea area A1 The radiotelephone coverage of VHF coast stations...

The collective set of systems that enables positioning devices to calculate latitude & longitude. The system includes solutions including the GPS (US) and GLONASS (Russian) network of satellites.

The US-based system of satellites, able to determine the latitude and longitude of a receiver on Earth by calculating the time difference for signals from different satellites to reach the receiver. GPS is part of the GNSS solution for positioning used by chart plotters and other positioning devices.

An internationally agreed-upon set of safety procedures, communication protocols, and equipment designed to ensure that ships at sea can send and receive distress signals and safety information. The Global Maritime Distress and Safety System (GMDSS) was established by the International Maritime Organization (IMO) to enhance maritime safety and facilitate the efficient coordination of search and...

The mean solar time at the Prime Meridian in Greenwich, London, used as a global time standard. Greenwich Mean Time (GMT) is a timekeeping system that started at the Royal Observatory in Greenwich, London, and acts as a reference point for global time zones. It is based on the mean solar time at the Prime...

A type of map projection where the surface of the Earth is projected onto a plane from the centre of the globe, causing great circles to appear as straight lines. A gnomonic projection is a method of map-making that projects the surface of a sphere, such as the Earth, onto a flat plane. The projection...