The Global Positioning System (GPS) is a U.S. space-based global navigation satellite system. It provides reliable positioning, navigation, and timing services to worldwide users on a continuous basis in all weather, day and night, anywhere on or near the Earth.

GPS is made up of three parts: between 24 and 32 satellites orbiting the Earth, four control and monitoring stations on Earth, and the GPS receivers owned by users. GPS satellites broadcast signals from space that are used by GPS receivers to provide three-dimensional location (latitude, longitude, and altitude) plus the time.

Since it became fully operational on April 27, 1995, GPS has become a widely used aid to navigation worldwide, and a useful tool for map-making, land surveying, commerce, scientific uses, tracking and surveillance, and hobbies such as geocaching and waymarking. Also, the precise time reference is used in many applications including the scientific study of earthquakes and as a time synchronization source for cellular network protocols.

GPS has become a mainstay of transportation systems worldwide, providing navigation for aviation, ground, and maritime operations. Disaster relief and emergency services depend upon GPS for location and timing capabilities in their life-saving missions. Everyday activities such as banking, mobile phone operations, and even the control of power grids, are facilitated by the accurate timing provided by GPS. Farmers, surveyors, geologists and countless others perform their work more efficiently, safely, economically, and accurately using the free and open GPS signals.

Global Navigation Satellite Systems (GNSS) is the standard generic term for satellite navigation systems that provide autonomous geo-spatial positioning with global coverage. GNSS allows small electronic receivers to determine their location (longitude, latitude, and altitude) to within a few metres using time signals transmitted along a line-of-sight by radio from satellites. Receivers on the ground with a fixed position can also be used to calculate the precise time as a reference for scientific experiments.

As of 2009[update], the United States NAVSTAR Global Positioning System (GPS) is the only fully operational GNSS. The Russian GLONASS is a GNSS in the process of being restored to full operation. The European Union’s Galileo positioning system is a GNSS in initial deployment phase, scheduled to be operational in 2013. The People’s Republic of China has indicated it will expand its regional Beidou navigation system into the global Compass navigation system by 2015.

The global coverage is achieved by constellations of about 30 MEO satellites in different orbital planes. The actual systems use orbit inclinations of >50° and orbital periods of 12 hours (height 20,200 km).

Broadcasting is the distribution of audio and/or video signals which transmit programs to an audience. The audience may be the general public or a relatively large sub-audience, such as children or young adults.

The sequencing of content in a broadcast is called a schedule. As with all technological endeavours, a number of technical terms and slang have developed. A list of these terms can be found at list of broadcasting terms. Television and radio programs are distributed through radio broadcasting or cable, often both simultaneously. By coding signals and having decoding equipment in homes, the latter also enables subscription-based channels and pay-per-view services.

The term “broadcast” originally referred to the sowing of seeds by scattering them over a wide field. It was adopted by early radio engineers from the Midwestern United States to refer to the analogous dissemination of radio signals. Broadcasting forms a very large segment of the mass media. Broadcasting to a very narrow range of audience is called narrowcasting.

Cartography (in Greek chartis = map and graphein = write) is the study and practice of making geographical maps. Combining science, aesthetics, and technique, cartography builds on the premise that reality can be modeled in ways that communicate spatial information effectively.

The fundamental problems of cartography are to:

* Set the map’s agenda and select traits of the object to be mapped. This is the concern of map editing. Traits may be physical, such as roads or land masses, or may be abstract, such as toponyms or political boundaries.
* Represent the terrain of the mapped object on flat media. This is the concern of map projections.
* Eliminate characteristics of the mapped object that are not relevant to the map’s purpose. This is the concern of generalization.
* Reduce the complexity of the characteristics that will be mapped. This is also the concern of generalization.
* Orchestrate the elements of the map to best convey its message to its audience. This is the concern of map design.

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