• PC World
• »GPS

Key Features

Map coverage: Car-centric GPS models sold in the United States typically include detailed street maps for the entire country. It's like having an entire set of Thomas Guides for the U.S. localities packed into a box the size of an iPod. Some GPS vendors may include maps for Canada and Puerto Rico as well. And you can buy additional digital maps for various foreign lands. Nearly all of this electronic map data comes from two or three primary sources, so the information is quite similar, regardless of which model you purchase.

Handheld models are less homogeneous: Some can't display maps at all (instead they report your longitude and latitude, with a trail (or "track") of such coordinates to indicate where you've been; others let you load street maps and topographic maps, and a few can display downloaded satellite images. Maps are harder to read on the smaller screens that most handheld models have.

3D map view: Most car-centric models can display map data in 3D map view, also called bird's-eye view. As you travel along, the GPS map continually updates to show your current position and the surrounding terrain. Using a device that offers only a 2D view is like looking straight down at a 3-square-inch section of a typical paper map. 

A 3D view gives you a graphical representation of the view out of your windshield, but from an elevation of a couple hundred feet--something like a low-altitude Flight Simulator. The resulting map is easier and faster to interpret while you are driving.

Turn-by-turn directions: The raison d'être for any automobile-centric GPS units, turn-by-turn directions prompt you visually and with spoken instructions regarding when to turn right, when to turn left, and when to get on or off a freeway, from starting point to final destination. You simply use an on-screen keyboard to enter an address (usually with text that automatically fills as you enter the letters) and press the Go button. Do not attempt to do this while you're driving! Set up your trip before turning your key in the ignition.

The GPS device will take some seconds to calculate the route and point you in the right direction on its digital map. When driving, you must get these directions clearly and in timely fashion--not too early or too late, but at the right moment so you can safely prepare and execute your change in direction. Almost all car-centric models handle this task beautifully.

Most units deliver spoken directions through their built-in speaker, which needs to have sufficient volume and clear sound to overcome vehicle noise. A few models include a short-range FM transmitter for sending voice prompts though your car's audio system.

POIs: The Points of Interest feature consists of a database of locations and services--gas stations, hotels, parks, coffee shops, and so on--that you may want to consult during your travels. Most automobile-centric GPS units have millions of POIs in their database. But because businesses change even faster than roads do, POI lists tend to be less accurate than GPS street maps. Better POI lists provide phone numbers along with the names and locations of services. 

Touch screens: Recently car-centric GPS units have begun doing away with hard control buttons in favor of touch screens, which are faster and easier to use than mechanical buttons. By tapping on the screen, you can enter addresses, search for POIs, change screens, and alter various GPS settings. Touch screens also let you use virtual, intelligent keyboards, the most advanced of which make data entry extremely fast.

Need to add an address? Start typing the street name for a given city and the keyboard displays only the letters that make up a valid street name in that city. In most instances, the keyboard will disappear after you've entered three or four letters, and you're left with a short list of legitimate names. Entering a complete address in this way takes very little time.

You won't find touch screens on many handheld GPS devices because their (typically) smaller screens make tapping less efficient; as a result, handhelds often have far more complex controls.

Screen size and type: Screens on automobile-centric GPS models generally range from about 3.5 inches to 7 inches diagonally. Don't be too quick to dismiss a smallish display: A device with a well-designed screen and clear audio directions can work just fine. And models with smaller screens usually cost far less than their big-screen counterparts. Large screens do have obvious advantages, however: Bigger maps, more room for travel data (such as speed, direction, street labels), and roomier virtual keyboards may justify the extra cost for you.

Real-time traffic reports: Using a built-in or added-on FM receiver, a GPS with traffic report capability can receive signals from the Traffic Message Channel (TMC), a subscription service broadcast in selected cities. Traffic tie-ups and construction information appear on your GPS map, enabling you to avoid delays by choosing an alternate route. Some GPS models will automatically reroute you, based on the TMC reports.

Media card slots: GPS devices store all of their mapping and POI data in one of two ways: on a built-in hard drive, or on flash memory cards, typically Micro SD Cards. Hard-drive models tend to be faster at calculating routes and searching for POIs, but media cards are more durable. Though hard-drive-based models don't require a media card slot, such a slot is useful for updating maps and backing up addresses and favorites.

Channels: Channels determine the number of satellite signals the GPS can receive simultaneously. Low-costs models typically have 12 channels, while high-end models may accommodate up to 24. Roughly speaking, the greater the number of channels, the better the device's accuracy.

Waypoints: Waypoints are specific geographic locations, described by longitude and latitude, that you have recorded in your GPS unit. Press the waypoint record button on your GPS at a trailhead, and you can always find your way back to your car. Waypoints are rarely used with automobile-centric GPS devices, but they're essential for handheld models. Low-cost units will store relatively few waypoints; high-end models will store hundreds, permit you to manage them within the GPS, and enable you to label them as you wish.

Tracks: Another centerpiece of handheld navigation is the Tracks feature. As you walk or drive though the countryside, your GPS device records and displays a breadcrumb trail of where you've been. This process lets you easily backtrack to your starting point; some models also let you download your track to your personal computer and view your travels on a topographic map. Print out the map and the track for a permanent record of your journey. As in the case of waypoints, low-end models offer limited track storage, while high-end models store many and allow you to identify them by adding custom names.