Active Log - The segment of a route currently being traveled.

Backtrack - Navigation of a route in reverse order from the last position fix in succession to the first. Reverse of navigating a route in normal sequence.

Bearing - For G.P.S. navigation, it generally refers to the compass reading to navigate from one position to another measured to the nearest degree. In traditional nautical navigation, it is referenced a differently in degrees from quadrants of the compass. See G.P.S. for Land Navigation by Michael Ferguson for more details on this topic.

Coordinates - A set of numbers that describes a given position for a given coordinate grid system. Examples of coordinate grids are Latitude/Longitude and Universal Transverse Mercator (UTM).

Course - The direction in degrees between two waypoints or the course indicated by a G.P.S. receiver when the "GOTO" function is activated.

COG - C - ourse O - ver G - round: The actual direction you (G.P.S. receiver) are traveling.

Datum - A reference system for vertical and horizontal positions. Different datums have different positions for the physical location of their origins, thus different datums will represent coordinates in different positions. Differences can be as much as a mile. All reliable maps that show coordinate systems provide Datum information.

Declination - The angular difference between True North and some other reference for north such as Grid North or Magnetic North.

Differential G.P.S. - A means of compensating for Selected Availability error in G.P.S. locating using radio transmissions.

Elevation - The distance above mean sea level usually in meters or feet.

Equator - The Latitude reference point for the Lat/Long grid system. Other positions of latitude are referenced as degrees of North Latitude if they are north of the equator and degrees of South Latitude if they are south of the equator. Also see Latitude.

ETA - E - stimated T - ime of A - rrival: The estimated time of your arrival computed at your present speed toward the destination.

ETE - E - stimated T - ime E - n route: The projected travel time it will take to arrive at your destination or waypoint.

GIS - G - eographic I - nformation S - ystem: A category of computer programs and applications that are used to organize, analyze and display geographic information.

GMT - G - reenwich M - ean T - ime: Time at 0° or the Prime Meridian passing through Greenwich England. A - lso Universal T - ime C - oordinated (UTC). In aviation Zulu Time.

G.P.S. - G - lobal P - ositioning S - ystem: A generic term for satellite based positioning system.

Grid - A system of horizontal and vertical lines used to chart specific position coordinates i.e. the Latitude/Longitude Grid system.

Grid North - The direction that north/south lines of a grid point.

Grid Zone - One of the 60 zones covered by the Universal Transverse Mercator (UTM ) grid system of navigation.

Heading - The direction that you are facing or traveling see Bearing.

Initialization - The initial orienting process that a G.P.S. receiver does when it is first turned on. If it is the first time the receiver has been turned on or if the receiver is more than a few hundred miles from the last location it was used, it will take some time or help from the operator by inputting or selecting from a menu the approximate location.

Landmark - A specific location or identifiable natural or man-made geographic feature. Also referred to as a waypoint in G.P.S. navigation.

Latitude - The angular distance north or south of the equator when using the Latitude/Longitude grid system. These latitude lines are parallel to the equator and often referred to as "Parallels".

Legend - Information on a map for such things as scale, datum, and other details.

MGRS - M - ilitary G - rid R - eference S - ystem: A metric grid system that is a subset of the UTM system. It uses letter pairs to represent 10km squares.

Magnetic Declination - The difference between True North and the direction that a magnetic compass points for a given location. Magnetic declination varies from place to place and can change as much as a degree in a year.

Magnetic North - The direction that a magnetic compass will point. Can be 10°, 15° or even more different than True North.

Mean Sea Level - M - ean S - ea L - evel: The average level of the ocean.

Meridian - A line of longitude going north and south from pole to pole measured in degrees from the Prime Meridian or 0°. See Longitude.

MOB - M - an O - verB - oard: A feature in G.P.S. receivers to quickly mark a given location as you are traveling. Some receivers then activate a GOTO navigation function to that waypoint.

NAD27 - N - orth A - merican D - atum of 1927: The datum used on most large scale USGS topographic maps.

NAD83 - N - orth A - merican D - atum of 1983: A newer datum than the NAD27. Almost identical to WGS84.

NAVSTAR - The name of the United States Department of Defense satellite navigation system.

Northing - A term used to denote positions north of the origin in the UTM coordinate grid system.

Parallel - A line of latitude. See latitude.

Position Fix - The calculated position of the current location by a G.P.S. receiver.

Prime Meridian - The reference line for Longitude in the Lat/Long grid system. All other meridinas of longitude are designated in degrees East or West of the Prime Meridian up to 189°. The Prime Meridian is 0° Longitude.

Route - A series of progressive waypoints stored in a G.P.S. receiver which can be activated and navigated.

Scale - The ratio between actual distance and that same distance represented in a map.

SA - S - elected A - vailability: The intentional error introduced in G.P.S. signals by the government to degrade accuracy.

SOG - S - peed O - ver G - round: The speed the G.P.S. receiver is traveling.

Topographic Map - A map that gives not only locations of roads, landmarks and other features, but also gives contour lines at different elevations to show valleys, hills and other topography of the area.

True North - The geographic north of the globe and represented on the Lat/Long grid by the lines of longitude or meridians.

USGS - U - nited S - tates G - eologic S - urvey: A part of the U.S. Department of Interior and the primary mapping agency for the U.S. government.

UTC - U - niversal T - ime C - oordinated: The time on which all G.P.S. signals are synchronized.. The same as Greenwich Mean Time.

UTM - U - niversal T - ransverse M - ercator: A metric grid system consisting of 60 zones to cover the earth’s surface.

VMG - V - elocity M - ade G - ood: The speed at which you are progressing toward the destination or the GOTO waypoint.

Waypoint - A location designated by a set of coordinates and stored in a G.P.S. receiver to be later used as a GOTO destination or as part of a route.

XTE - Cross Track Error: The amount deviated to the left or right from the true course.