Choosing a Car GPS Navigation System

Never get lost again. That's the promise of car GPS navigation system. With built-in maps and turn-by-turn directions, you can't get lost, even if you miss an exit or turn left instead of right. In large cities like Los Angeles and New York, an auto GPS can give you the expertise of a veteran cabbie when it comes to getting around, and some systems will even help you avoid traffic.

How Do Global Positioning Systems Work?
The global positioning system (GPS) was developed by the US military as a way to coordinate troop and vehicle movements. GPS navigation was later opened to marine craft for navigation, and finally to a range of devices for cars, motorcycles and hikers.

GPS locates your position within a few feet anywhere on Earth thanks to satellites in the sky. There are 24 active satellites orbiting the Earth, and if your vision was strong enough, you'd be able to see at least four of them from nearly any point on the planet.

A GPS navigation system communicates with these satellites to triangulate your position. By sending radio signals to three satellites, the GPS can measure its distance from each one and tell you where you are. Auto GPS navigation systems take this information and overlay it on built-in maps to provide driving directions.

Higher-end car GPS navigation systems have additional receivers that can talk to more satellites, and they can provide better performance if there's a lot of tall buildings around. GPS struggles in tunnels and dense urban areas where concrete interferes with its radio signals; you should choose car GPS navigation with the extra receivers if you'll be driving in areas with a lot of skyscrapers or the mountainous regions of the Rockies.

Screens and Mounting
An auto GPS navigation system uses an LCD screen to display maps and directions. Most models have touch-screens that let you program your destination. You'll then be guided with spoken turn-by-turn directions so you can keep your eyes on the road.

Screen sizes vary and they do affect price, so you'll want to get the biggest screen that you can afford, although this should be secondary to the quality of the radio receivers and the number of satellites the GPS can use. Look for a high-contrast screen that won't get washed out in bright sunlight.

You can have the GPS installed directly into your dashboard, if your car has the space. In-dash GPS navigation must be professionally installed, but these units are much harder to steal and can be integrated with some cars to provide controls directly on the steering wheel.

A more common choice is a portable unit that attaches to your dashboard or windshield. If you go the portable route, be sure that the GPS is easy to reach while you're driving. You should be able to keep one hand on the wheel while you operate it.

Check the navigation menu as well, since you don't want to be distracted with GPS operations while you're driving. Your most frequently used functions should be no more than two screen taps away. Better still are voice-activated devices that enable you to keep your hands on the wheel at all times.

Mapping Your Route
Car GPS navigation systems all include a basemap, which is a large-scale view of the world around you. Basemaps include major highways and large cities, but they lack local roads. To get the local view, you'll need region maps that show side streets and downtown grids. When you buy a GPS, it's usually loaded with the region map for your area. Additional region maps can be downloaded to your GPS from your computer. You'll find a variety of free maps available online, or you can get specialized maps from the manufacturer. For example, Garmin offers a series of maps for Garmin GPS systems.

Maps need memory. A single metropolitan area takes up about 8MB of storage space. GPS navigation systems have a small amount of built-in memory for frequently used maps, and you can supplement this with Compact Flash (CF) or Secure Digital (SD) cards that can be swapped on the road or in the field as needed. Memory cards are a great way to store maps that you only use occasionally. Find out what type of memory cards your GPS uses, and get a compatible card reader for your PC so you can download maps from the Web.

Traffic receivers do more than just provide alternate routes during rush hour jams-they also track construction and weather-related detours. There's a monthly fee for this service, and shopping around can save you money. Delphi GPS navigation systems offer a traffic service antenna for $200 with no additional monthly fees. If you get a GPS with XM satellite radio, you can take advantage of XM's traffic service for an extra $13 a month. Other services can run as high as $50 a month, which makes the question of traffic sorting with a GPS a costly proposition. Think about how much you need this feature, and compare car GPS navigation systems to find out which traffic services they support.