GEOG 160
Mapping Our Changing World

5.7 Glossary


Accuracy: How close or far a measurement is from the true or accepted value. Close measurements are more accurate than those that a further from the real value.

Additive Correction: A singular amount that is added to or subtracted from a series of measurements as a means to reduce systematic error.

Azimuth: Measurements of direction in terms of degrees, ranging from 0° to 360°.

Bearing: An angle less than 90° within a quadrant defined by the cardinal directions.

Closed Traverse: A measurement of distance between a single point and an unknown point that begins and ends at the same location.

Control Segment: The segment of the Global Positioning System that is comprised of ground stations that monitor and analyze satellite orbits and send corrections as needed.

Data Quality: The fitness of data for their intended use.

DGPS: Differential Global Positioning Service. DGPS offers enhanced locational measurements through the use of radio beacons that provide corrections.

Differential Correction: The use of control station to acquire a differential calculation which is then sent to local receivers to increase the accuracy of their measurements.

Dilution Of Precision (DOP): A factor that multiplies the uncertainty associated with User Equivalent Range Errors, based on the current configuration of viewable satellites. A DOP of 1 represents an ideal scenario, though real-world experiences seldom notice a DOP less than 2.

Environmental Characteristics: Variations in temperature, gravity, and magnetic declination that contribute to measurement errors.

GPS: The Global Positioning System.

Human Errors: Mistakes, improper use of equipment, and poor judgment that leads to measurement errors.

Instrument Errors: Errors that result from limitations related to the finite resolution of measuring equipment and its application in an infinite, continuous space.

Multipath Error: GPS errors that result from poor view of orbiting satellites, which are affected by buildings, valleys, the atmosphere, and other elements that can block, reflect, or refract GPS signals.

Open Traverse: A measurement of distance between a single point and an unknown point that begins and ends at different locations.

Precision: How reliably similar measurements can be taken with respect to variation and resolution.

Proportional Correction: Identifying a trend and applying the proper equation to adjust measurements in an attempt to correct inconsistent systematic errors.

Random Errors: Errors that do not follow a trend and are off by various amounts with no discernable pattern.

Resolution: The smallest measurement unit that can be detected or represented. High resolution refers to smaller units while low resolution refers to larger, and therefore fewer, units of measurement in the same space.

Satellite Ranging: Calculating distances from observable satellites based on their internal clocks and the amount of time taken for a signal to reach a corresponding receiver.

Space Segment: The segment of the Global Positioning System that is composed of a constellation of satellites following a precisely defined array of orbital planes.

Systemic Errors: Errors in measurement that follow a systematic and calculable trend.

Theodolites: Electronic equipment used in surveying for precise and accurate measuring of angles.

Total Station: A surveying instrument that is capable of electronic distance ranging as well as the angle measuring abilities of theodolites.

Triangulation: A trigonometric process of determining the position of unknown points based on the angles and distances calculated from a known point and a determined baseline.

Trilateration: The use of distances from known points to determine the position of an unknown point. At least three known locations are required for two-dimensional trilateration, while four known distances allows 3-dimensions (horizontal plus elevation).

User Segment: The segment of the Global Positioning System that is made up of devices that can receive satellite signals and the humans who operate these devices.

Wide Area Augmentation System (WAAS): The system of ground reference stations and geostationary satellites that enable the calculation and broadcast of corrected GPS signals.