Buying guide: GPS units and sat navs

Need help shopping for a GPS unit? Deciding between sat navs from Garmin, TomTom and Navman? Read our handy buying guide

Jargon Busters: GPS units

Atomic clock: Atomic clocks are the basis of a GPS navigation system. The GPS master clocks are atomic clocks at the ground stations, and each of the GPS satellites has an on-board atomic clock.

Geographic location: A geographic coordinate system enables every location on the Earth to be specified by the three coordinates of a spherical coordinate system that is aligned with the spin axis of the Earth.

GPS: GPS stands for Global Positioning System. More than 24 GPS satellites orbit the Earth, transmitting signals that allow GPS receivers to determine the receiver's location, speed and direction.

Latitude: Latitude gives the location of a place on Earth north or south of the equator. Latitude is an angular measurement in degrees, ranging from 0° at the Equator (low latitude) to 90° at the poles (high latitude).

Longitude: Longitude describes the location of a place on Earth east or west of a north-south line called the Prime Meridian. Longitude is given as an angular measurement ranging from 0° at the Prime Meridian to +180° eastward and -180° westward.

MicroSD card: A miniature version of an SD card, most commonly used in mobile phones, smartphones and some portable GPS units.

POI: POI Stands for Point of Interest. A POI is a specific point location that someone may find useful or interesting. The term is widely used in GPS navigation software.

Satellite: A satellite is any object that orbits another object. Satellites can be manmade (such as those used for GPS) or may be naturally occurring.

SD card: SD stands for Secure Digital. An SD card is a flash memory card format developed by Matsushita, SanDisk and Toshiba for use in portable devices. An SD card can be used in a number of digital cameras and GPS units.

SUNA Traffic Channel: The SUNA Traffic Channel broadcasts live traffic information directly to a compatible GPS navigation system. This enables users to be redirected around accidents or traffic build-up.

Touch screen: A touch screen is a display that has the ability to both display and receive information. This allows display to be used as an input device, eliminating the need for physical buttons.

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