What kind of coverage do you want, and can you download more POIs? If you don't have an auto-dimmer, can you always see the 3D mapping? And should you insist on dynamic re-routing? This jargon buster should help you find out.
Anti-glare - See Auto-dimming.
Auto-dimming - A system, using a built-in sensor, that automatically reduces (or increases) the amount of light emitted by the screen to take account of the light conditions outside, to aid clarity.
Bluetooth - Wireless technology that allows mobile phones, computers etc to communicate with each other over short distances, without cables.
Car navigator - Another name for a sat nav.
Coverage - See Map coverage
Cradle - Another term for the mount by which the sat nav unit is fixed to the windscreen of dashboard.
Custom POIs - Specialist companies gather and publish sets of Points of Interest (POIs), which you might be able to purchase and load onto your sat nav. These are known as Custom POIs. See Point of Interest.
Dock - Another name for a mount (to attach the sat nav unit to the windscreen or dashboard).
Dynamic re-routing - If you miss a turn, or decide to change your route while driving, the sat nav unit will automatically recalculate your route from your present position. Also known as 'dynamic route recalculation'.
EGNOS - European Geostationary Navigation Overlay Service, a land-based navigation system created to augment GPS accuracy, and used in the newer handheld GPS receivers. The American equivalent is WAAS.
Embedded flash memory - A memory device that stores information when the power supply is turned off.
ETA - Estimated Time of Arrival; also referred to as 'time to destination'.
Expansion slot - A slot in the sat nav unit that allows you to expand its capabilities or data by inserting a card.
Fuel and park buttons - Dedicated buttons on the sat nav that tell you where the nearest petrol stations and car parks are located.
Global Positioning System (GPS) - The network of 29
GNSS - Global Navigation Satellite System.
GPRS - General Packet Radio Service: this upgrades 2G (second generation) mobile telephones to 3G (third generation).
GPS - Global Positioning System.
Handheld battery-operated unit - Some sat navs are designed for walkers and runners (as opposed to vehicle use), and are powered by batteries. Car sat navs can perform the same function when removed from the car, if fitted with batteries.
Hard install - Sat nav units that are fixed into the car, often by the car-manufacturer; the opposite of 'portable sat navs'.
Itinerary planning - This allows you to plan a whole a journey, involving a sequence of destinations, by inputting the data into your sat nav unit before setting out.
Li-ion battery - A lithium-ion battery: a common form of rechargeable battery.
Live traffic information - A live link to traffic reports, supplying up-to-date information about road conditions and traffic jams ahead; some sat navs will automatically change your route to take account of any problems.
Map coverage - The geographical area covered by the maps that are supplied as part of your sat nav package.
MP3 capability - The sat nav is able to transmit sound from an MP3 player, such as an iPod, if linked by a cable.
Navigation audio prompts - The spoken directions given by your sat nav to guide you; the same as voice direction/instruction.
POI - See Point of Interest.
Point of Interest (POI) - Most sat navs also supply details of the location (usually represented by icons) of various places that could be useful to you on your route. These are known as Points of Interest (POIs). They might include: petrol stations, car parks, vehicle repair centres, cashpoints, shops, restaurants, hotels, museums, post offices, emergency services, parks, cinemas and other places of entertainment.
Portable sat nav - A sat nav unit that you can take out of the car, carry around with you, operate on batteries, and use in any vehicle you choose.
Pre-loaded safety camera locator - A programme, already installed in your sat nav unit, which alerts you to upcoming safety cameras (speed and red-light cameras) along your route.
RDS-TMC - Radio Data System - Traffic Message Control: a service that provides the delivery of traffic information to an international standard.
Real-time traffic information - See Live traffic information.
Receiver - Your sat nav unit contains a receiver capable of receiving signals from orbiting satellites.
Red-light camera - A traffic control camera stationed at traffic lights to record infringements of the red-light instruction.
Road exclusion - The facility to exclude certain roads or places along your route when requesting an itinerary from your sat nav unit (for instance, when you know of congestion on a local road caused by roadworks, or want to avoid a toll bridge).
Route update - See Dynamic re-routing.
Safety camera - The polite term for a speed camera or a red-light camera.
Sat nav - Satellite Navigation. The term is now also generally used to refer to the sat nav unit itself.
Screen size - The size of the screen measured diagonally across it. Screen sizes are typically 3.5" (inches) or 4", or 4.5" for wide-screen models.
SD memory cards - Secure Digital memory cards, a standard form of memory card used in digital devices.
Searchable postcode digits - One way to find a destination on your sat nav unit is to input the postal address, with the street name; but it is far quicker and more precise to use a postcode, if your unit permits this - and best if it allows you to input the full postcode, when all seven of the postcode digits are used (and hence 'searchable').
Speed camera - A camera that monitors traffic speeds, and records infringements.
Stand-alone battery time - The amount of time that a sat nav unit will operate when powered only by the battery (e.g. when you take it out of the car and use it to guide you to your destination on foot).
3D mapping - 2D (two-dimensional) maps give you an overhead view of a location, like a traditional paper map. 3D maps give you a schematic, angled view of the route ahead of you, as if seen from the air above you. 3D mapping makes it easier to visualise your next move along the way.
Touch-screen - A technology that allows you to input instructions by using a fingertip to select data on the screen. This is rather easier that using the buttons on a keyboard.
Traffic alerts - Warnings about traffic problems ahead. See Live traffic information.
Voice direction/instruction - The spoken directions given by your sat nav to guide you.
WAAS - Wide Area Augmented System, a
Waypoints - Points in your itinerary that you may wish to specify in order to get your sat nav unit to select the route that you want to take.