- C -
C/A Code - the standard (Course/Acquisition) GPS code used by most GIS level GPS receivers. Also known as the civilian code.
Carrier - the signal that carries the C/A Code from the satellite to the GPS receiver.
Carrier-aided Tracking - a signal processing technique that uses the GPS carrier signal to achieve an exact lock on the pseudo random code generated by the GPS satellite. Carrier-aided tracking is more accurate than standard C/A Code tracking.
Channel - a channel of a GPS receiver consists of the circuitry necessary to track the signal from a single GPS satellite.
Cycle Slip - a loss of continuity in the measured carrier beat phase which results from a temporary loss of lock on a GPS satellite.

- D -
Differential Correction - the technique of comparing GPS data collected in the field to GPS data collected at a known point. By collecting GPS data at a known point, a correction factor can be determined and applied to the field GPS data.
Dilution of Precision (DOP) - an indicator of satellite geometry for a unique constellation of satellites used to determine a position. Positions tagged with a higher DOP value generally constitute poorer measurement results than those tagged with lower DOP.
Dynamic Positioning - the process of collecting GPS data while the GPS antenna is in motion. Often associated with Line or Area Features.

- E -
Ephemeris - the predicted changes in the orbit of a satellite that are transmitted to the GPS receiver from the individual satellites.
Ephemeris Errors - errors which originate in the ephemeris data transmitted by a GPS satellite. Ephemeris errors are removed by differential correction.

- F -
Feature - the object which is being mapped for use in a GIS system. Features may be points, lines or areas.
Featuring - the process of collecting GPS and GIS information simultaneously.

- G -
Geographic Information System (GIS) - a mapping system which combines positional data with descriptive information to form a layered map.
Global Positioning System (GPS) - a system for providing precise location which is based on data transmitted from a constellation of 24 satellites

- L -
L-band - the group of radio frequencies which carry the GPS data from the satellites to the GPS receivers.

- M -
Multipath - the interference to a signal that has reached the receiver antenna by multiple paths; usually caused by the signal being bounced or reflected. Signals from satellites low on the horizon will have high multipath error. Receivers that can be configured to "mask out" signals from such satellites can help minimize multi-path.

- P -
Pseudorange - an uncorrected measurement of the distance between a GPS satellite and a GPS receiver determined by comparing a code transmitted by the satellite to a code generated by the receiver.

- R -
Residual - a quality indicator for a GPS position that is determined during the differential correction process. Indicates uncorrectable error. High residuals are not desirable.

- S -
Satellite Constellation - the group of GPS satellites from which data is used to determine a position.
Static Positioning - the process of averaging GPS positions taken successively over a period of time with a stationary antenna to increase accuracy.

- V -
Value - descriptive information about a Feature. Values can be thought of as the answers to the questions posed by Attributes.