Terminology

Accuracy Warning System - A very important feature that lets the user know if the accuracy of the system has degraded (for instance if something is suddenly blocking access to some of the satellites that had been in use).

Database - Many receivers have built-in collection of permanent waypoints for useful locations.

Data Port - Most receivers have a data port so that data can be fed back and forth from a computer.

Datum (Map Datums) - A datum is a model of the surface of the earth based on a surveyed network of physical points. In the U.S., the most common is the North American Datum of 1927 (NAD27). This datum is used on USGS and USDAFS (USDA Forest Service) maps along with many other government and private maps.  There are over a 100 other datums in use throughout the world.

Differential GPS - This is a way of overcoming the inaccuracy of the SA-degraded C/A code by using a DGPS beacon transmitter along with the GPS Receiver. The beacon is placed on a surveyed, known point. This transmitter continuously computes the difference between its known position and its GPS position, then transmits the correction. The DGPS enabled receiver then corrects its own position.

GPS - (Global Positioning System) A system of 21 operational satellites and 3 spare (non-operational) satellites orbiting 12,000 miles above the earth.

Plot Screen - Most GPS receivers have screens showing the receiver's position along with direction and distance from nearby waypoints.

Receiver Channels - This term refers to the number of satellites from which the receiver can receive information.

Route - A path determined when multiple waypoints are used together.

USGS Topographic Maps - The most accurate maps published in the United States.  These maps use contour lines to show elevation and shape of the land.  They can be obtained on paper or as data sets to load into a GPS receiver.

UTM - (Universal Transverse Mercator) A special grid map adopted by the National Imagery and Mapping Agency (NIMA) for military use throughout the world.  This grid is arranged so that the earth is divided into 60 north-south zones (each is a strip 6 degrees wide in longitude).  These zones are numbered consecutively beginning with Zone 1 between 180 and 174 degrees west longitude.

WAAS - (Wide Area Augmentation System) A DGPS system being built by the Federal Aviation Administration (FAA) to improve the accuracy of GPS for aircraft en route. A similar system Local Area Augmentation System (LAAS) will be used for precision-instrument approaches so that it can be used by aircraft guidance to the runway in bad weather.

Waypoints - Many GPS receivers can store a coordinate with a description used for navigation.