Maps GPS Glossary - P

packet - A unit of data that is routed between an origin and a destination on the Internet or any other packet-switched network.

parallel of latitude - An imaginary line circling the surface of the earth that is parallel to the equator; a line of latitude.

paramo - A treeless alpine plateau of the Andes and tropical South America.

patch antenna - An antenna based on a plated section of metal on a circuit board and its associated electronics used for receiving GPS signals.

PCMCIA - Personal Computer Memory Card International Association - A standard for a credit card-size memory or input/output device that fits into a notebook, laptop or personal computer.

PDA - Personal Digital Assistant - A small mobile hand-held device that provides computing and information storage for personal or business use, often for keeping calendars and address information.

PDOP - See Geometric Dilution of Precision

photogrammetry - The process of making maps from photographs, usually aerial photographs.

planimetric map - A map that shows only the horizontal positions of features represented, as opposed to a topographic map.

plat - A map showing planned or actual features such as streets and building lots.

PNG - Portable Network Graphics - A file format for bitmapped graphic images approved by the World Wide Web Consortium as a replacement for GIF files. GIF files use a patented data compression algorithm; PNG is patent- and license-free.

PNT - U.S. Space-Based Positioning, Navigation, and Timing Policy. - A national policy that took effect on December 8, 2004 that establishes guidance and implementation actions for space-based positioning, navigation, and timing programs, augmentations, and activities for U.S. national and homeland security, civil, scientific, and commercial purposes.

Pocket PC - Software for personal digital assistants (PDAs) and any PDA that uses that software.

position error - The distance that the displayed position is off by.

position fixing - Using a coordinate system to determine a point on a map's location.

Positional Dilution of Precision - See Geometric Dilution of Precision

PPS - The highest level of military dynamic positioning accuracy provided by GPS, using the dual-frequency P-code.

prefecture - The district administered or governed by a prefect (an administrative official).

prime meridian - A line of longitude at 0 degrees that runs through Greenwich, England; used as the origin for measurements of longitude.

prismatic compass - A compass that allows the user to see the compass face and distant locations at the same time.

PRN - Pseudo-random Noise - A digital signal which appears to be randomly distributed like noise, but is actually not random. Each NAVSTAR satellite has its own code.

Projection - Representing the two-dimensional curved surface of the earth on a plane; the method used to transpose a map of the earth onto a flat surface.

pseudolite - pseudo-satellite - A ground-based differential GPS receiver that simulates the signal of a GPS satellite and can be used for ranging. The data portion of the signal may also contain differential corrections that can be used by receivers to correct for GPS errors.

pseudorandom code - The identifying signature signal transmitted by each GPS satellite and mirrored by the GPS receiver in order to separate and retrieve the signal from background noise.