Other Important Features to Look For
Accuracy: Almost any GPS model sold today can display your location with astounding accuracy. But streets and businesses change, so the accuracy of that information depends on how up-to-date it is. A less-reputable GPS vendor could cut the cost of its low-end products by providing outdated mapping data. Check whether the vendor provides regular map and POI updates, and how much they cost. Some vendors offer free updates for a fixed time, or even the lifetime of the device; others charge up to $100 or so for each update. Some GPS devices come with access to online communities where you can share mapping information, and download information that other users have provided.
Usability: Car GPS devices can be more distracting than a cell phone to a driver. The maps must be readable at a quick glance, so they must have high-quality graphics and avoid the clutter of nonessential information. For the same reason, the device's touch-screen controls must be well organized and clearly labeled. Some vendors make it easy to add an impromptu pit stop along the programmed route, but many do not.
Reflective screens: Bright, direct sunlight can overwhelm a GPS unit's built-in screen backlighting, rendering your maps unreadable. On better units, a reflective coating behind the screen uses sunlight to brighten the display, enabling you to read your maps quickly in any lighting.
Mounting bracket kits: If you plan to use your GPS unit mostly in the car, look for a kit that includes a sturdy mounting bracket and both AC and 12-volt power adapters.
Because some states ban the use of windshield-mounted GPS devices, it's important to know your state's applicable rules before you buy. The merchant selling you the device may be able to provide you with an alternative mount as necessary--perhaps an air-vent mount or beanbag mount.
Power supply: GPS devices designed primarily for in-car use plug into the car's 12-volt power port. Out on the trail, however, a handheld GPS device with batteries is mandatory. For short trips, a model with built-in rechargeable batteries will do. But if you take to the hills for hours or days at a time, you should pick a unit that runs on replaceable AA or AAA batteries--preferably rechargeables. Small GPS units typically save weight and space by using two AAA cells, but they may last for only 4 or 5 hours on one set of batteries. Larger handhelds use up to four AA cells (which means more weight) but run for as long as 12 hours per set.
Weight: If you expect never to use your GPS unit outside your car, weight isn't an issue. But the situation is quite different if you're the one carrying the device. Handheld models range in weight from a couple of ounces to nearly a pound--not counting the weight of extra batteries.
Dead reckoning: If you often drive in cities filled with tall buildings, GPS signals can be spotty, and your location accuracy may plummet. And of course, missing a turn because the GPS doesn't know exactly where you are can be bad news. Some higher-end GPS models include a feature called dead reckoning, which uses interpolation to fill in brief gaps caused by lapses in the GPS signals. The procedure involves estimating your speed and direction, and updating the map accordingly. But don't be surprised if its accuracy is poor.
Bluetooth: Many high-end (and even some midrange) GPS devices come with support for Bluetooth. This allows you to pair your GPS device with a compatible cell phone and make hands-free calls using the GPS's speaker.
Music and video players: You won't be watching videos while driving, but you might want to listen to some tunes. Many high-end GPS devices will play back music stored on a removable card. They may also show photos.
FM transmitter: Some GPS devices include an FM transmitter that allows you to reroute all of the audio--including the spoken directions and any music you instruct the device to play--to your car stereo.
XM Radio support: Support for XM Radio isn't essential for navigation, but it's nice to have when you're on the road for hours or days. XM Radio is a subscription service and is found mostly in more-expensive GPS models.
Internet connectivity: This feature is still rare on GPS devices, but it can be convenient. It allows you to send addresses to your GPS device via the Web and helps you find information specific to your location, such as gas prices.
With GPS devices becoming more popular, vendors are continuing to differentiate their products through adding and improving features. The increased competition means you'll find GPS devices that are cheaper than ever but also do more than ever. Expect models with more and more extras--music and video players may be just the tip of the iceberg. Some high-end features will trickle down to lower-cost devices, too. Most important, though, GPS devices will continue to get you where you need to go, planning your routes better than they did before.