Glossary
Accuracy
How close your GPS position is to the actual location on the Earth with respect to a particular datum.
Acquisition time
The time it takes for a GPS receiver, upon power-up, to acquire enough satellites for the GPS receiver to compute a position.
Almanac
A “bus schedule” of the satellite orbits so the receiver knows roughly when/where a particular satellite will be in its orbit at a given time. It’s broadcasted by each satellite for all satellites and also includes information about the healthiness or unhealthiness of each satellite.
Antenna
A GPS patch or helical antenna tuned to the GPS frequency (typically L1 – 1,575Mhz).
Bluetooth
A short-range (typically 10 meters or less) wireless communications technology that is low power, low cost, robust and moderately secure. It allows for a wide variety of devices to communicate with each other.
Bearing
A direction expressed with respect to true or magnetic north.
Cartography
The technique of making maps and charts. GPS is used to help create maps, and also commonly used to navigate using digital background maps.
Channel
With respect to GPS, one channel is allocated to track one satellite. Thus, a typical 12-channel GPS receiver is capable of tracking up to 12 GPS satellites.
Cold/Warm start
A GPS receiver powering on without a current almanac is a cold start. A GPS receiver powering on with a current almanac is a warm start.
Coordinates
Geographic coordinates are a pair (usually latitude/longitude) of values with respect to a particular datum (usually WGS-84) that define a location on the Earth.
Course/heading
The direction of travel with respect to true north…as in current bearing. Often used with GPS when navigating to a waypoint.
Crosstrack error (XTE/XTK)
The amount of error, left or right, that you’ve deviated from the correct heading.
Datum
A mathematical model of the Earth that has been established by a collection of points based on their latitude and longitude. The datum used by GPS is WGS-84.
ETA (Estimated Time of Arrival)
The estimated time you will arrive at your destination based on your current speed and heading.
Geocaching
GPS-based, outdoor hunt where the seeker is provided latitude/longitude coordinates of a cache and challenged to find it.
Geostationary satellite
A satellite whose orbit is in line with the equator (0 degrees latitude) and thus remains stationary with respect to the Earth’s surface. WAAS/EGNOS broadcasting satellites are geostationary.
Geotag
Attaching geographic coordinates to media and multimedia such as photos, news feeds, images, etc. to facilitate a geography-based search engine.
GMT (Greenwich Mean Time)
GMT is a legacy version of UTC time (Coordinated Universal Time). It is the zero-point reference when referring to time zones. Also referred to as Zulu time.
GPS Week
A new GPS week starts every Saturday night at midnight. The GPS week number is the number of weeks that have elapsed since January 6, 1980, about the time that GPS satellites were modified to broadcast the GPS Week number.
Hand-held
A specific type of GPS receiver, usually with generic features and functionality as opposed to a GPS receiver with specific functions for mapping, aviation navigation, nautical navigation, etc.
Heading
The direction of travel with respect to true north…as in current bearing. Often used with GPS when navigating to waypoint.
Latitude/Longitude
A system of equatorial and meridian lines that comprise a coordinate system from which one can locate unique geographic positions on the Earth.
Mean Sea Level
The average height of the sea with respect to historical data.
Moving map
A digital map in which the center of the screen represents your location while the digital map underneath your position moves as you move.
MPP
Meters per pixel. Used to determine scale of digital raster maps.
NAVSTAR
NAVigation Satellite Timing and Ranging. Another name for GPS.
NMEA
National Marine Electronics Association. The NMEA 0183 standard is used on virtually every GPS receiver as a standard data transmission protocol between GPS receivers and other electronic instruments.
PDOP
Position Dilution of Precision. A value that defines the quality of the satellite constellation your receiver is tracking. A good-quality constellation is one where satellites are widely separated as opposed to “bunched”. A good “PDOP” is in the 2-4 range.
POI
Point of Interest. A specific point or location that someone might find interesting. Commonly used in navigation systems, standard POIs are locations such as restaurants, gas stations, rest areas, parks and schools.
PND
Portable/Personal Navigation Device. A GPS receiver that is most commonly optimized for vehicle navigation. Such devices include a detailed street-map database, Points of Interest (POIs) and software that provides the user turn-by-turn directions to a specific destination.
Position fix
A coordinate, typically latitude/longitude, computed by your GPS receiver.
PRN
Pseudo Random Number. A unique number that identifies a specific GPS satellite your GPS receiver is tracking. Each GPS satellite broadcasts its own “ID code” commonly referred to as the PRN.
Real-time traffic
Information that is sent, in real-time or near real-time, to your GPS navigation system to alert you of traffic delays along your path of travel.
Route
A series of waypoints, loaded in your GPS receiver, that define a path of travel to your destination.
SD card
Secure Digital memory card. A very small, high-capacity, standardized memory card for sharing digital content such as digital maps and digital photographs.
Sensitivity
A measurement of the ability of a GPS receiver to acquire and track GPS signals. A highly sensitive GPS receiver would be able to acquire and track GPS signals in weak signal environments.
SOG
Speed Over Ground. The speed in which the GPS receiver is moving with respect to the ground as opposed to airspeed or nautical speed.
TTFF
Time To First Fix. The amount of time it takes a GPS receiver to compute its position from a warm start (current almanac, known position, approximate time).
Topography
The surface and features of a particular area, typically presented as a detailed map. For example, a US Geological Survey 1:24000-scale topographic map.
Track log
Synonymous to a “bread-crumb” trail of where you’ve traveled based on how often you’ve set the GPS receiver to record.
True North
The direction of the North Pole. GPS operates with respect to true north, as opposed to magnetic north where compasses are oriented. The difference between the two varies depending on where you are located.
2D/3D
A 2-dimensional GPS position only includes horizontal coordinates. This type of position can be determined by tracking only three GPS satellites. A 3-dimensional position includes elevation in additional to horizontal coordinates. To determine a 3D position, a GPS receiver needs to track at least four GPS satellites. 2D/3D also are commonly used to describe map viewing perspectives on portable navigation devices (PNDs) and car navigation systems. In that context, 2D describes a birds-eye or “plan” view of the map while 3D describes an oblique view.
Update rate
The frequency in which a GPS receiver updates its position. The typical update rate is once a second (1Hz). Some receivers have an update rate of twenty times per second or more (20Hz).
USB
Universal Serial Bus. A standard serial bus interface that was originally designed for computers, but has migrated to devices such as GPS units, portable hard drives, MP3 players and mobile phones.
WAAS/EGNOS
Wide Area Augmentation System/European Geostationary Overlay System. Augmentation systems designed to improve the integrity and accuracy of GPS positioning. WAAS is the North American system. EGNOS is the European system.
Waymark
A waypoint with specific information about the location with respect to its waymark category such as a recreation area, services, cost, hours of operation, etc.
Waypoint
A destination point or point along a route. Waypoints can be created either by importing from a database, entering via keyboard or recording with a GPS receiver.