Types of GPS

Sizing up reviews for auto GPS

This report on auto GPS covers devices for in-car navigation. These differ from handheld GPS receivers meant for hiking and camping. Auto GPS systems have much larger screens, spoken directions and highway maps. Auto GPS units are larger and heavier than handhelds, and they aren't known for long battery life. However, all aftermarket auto GPS units are somewhat portable, with some marketed as crossover devices. See our companion report on handheld GPS to learn about units designed primarily for outdoor pursuits.

We found several rich sources of auto GPS reviews, including GPS enthusiast websites. One of these, GPSMagazine.com, sets the standard for GPS reviews. Every feature is tested, and each review shows readers exactly what they will experience using the product. The site includes a forum, a buyer's guide with quick recommendations and a lengthy list of auto GPS units to avoid because of their outdated technology.

GPSTracklog.com and GPSLodge.com are other enthusiast sites with very good coverage of the latest auto GPS. Reviews at other magazines and websites generally lack the detail of those found at enthusiast sites, but some do much better than others. For example, PC Magazine is very up-to-date with its GPS reviews, and its ratings and awards make it very clear which ones editors determine to be best. PC World and Laptop magazine have recently stepped up their GPS reviews, including critical reviews of poor-performing models. Consumer Reports rates and ranks 48 portable auto GPS systems in its latest update. Although the report has much less depth than the best review sources, the opinions are unquestionably unbiased, and GPS systems are clearly ranked from best to worst.

Finally, when reading older reviews of GPS systems, it's important to remember that some once favorably reviewed auto GPS systems are technologically out of date, although you can still buy them at retailers. GPSMagazine.com lists units to avoid, and most earn that distinction for this reason.

How GPS works

GPS (Global Positioning System) is a navigation technology that provides precise time and location data by using 24 NAVSTAR (Navigation Satellite Timing and Ranging) satellites. Each satellite completes one orbit of the Earth every 12 hours. They are positioned at an altitude that allows them to cover the same ground once every 24 hours (minus four minutes).

Each satellite carries an extremely accurate atomic clock and transmits both its position and a time signal, which can be picked up by a GPS receiver. Since a GPS unit can receive data from multiple satellites, and since each satellite provides information that is appropriate to its own location and distance, the GPS unit performs the necessary calculations and arrives at a position fix accurate to within about 15 feet. Many factors can have an impact on accuracy, including atmospheric conditions, buildings, tunnels and heavy foliage. However, reviewers say that the latest receivers greatly minimize those issues.

Handheld GPS vs. auto GPS

GPS receivers for the outdoor adventure market and for the automotive market are two different animals, although some can do double duty. Outdoors-oriented GPS receivers are made to resist the elements – most are rubberized and water-resistant. Handheld GPS units are also meant to be lightweight and easy to hold with one hand. They have smaller screens than auto GPS receivers do, and the screen isn't always in color. Handheld GPS receivers also emphasize battery life.

Auto GPS receivers are portable, but you wouldn't want to take them camping. They aren't water-resistant, and because of the large screen, they are much heavier than a handheld GPS (although the average weight is still less than half a pound). The big screen also saps battery life. Most auto GPS receivers can plug into a cigarette lighter. Auto GPS units come with highway maps and give audio directions. Handheld models sometimes only come with the most basic maps, and some don't come with maps at all. Auto GPS receivers also come with a windshield or dash mount, while most handheld GPS units don't.

Other options for in-car navigation include a smartphone with built-in GPS (see our report on smartphones) or a Bluetooth-equipped laptop or PDA. Some PDAs come with an integrated GPS antenna, while others can accept an accessory receiver. Laptops have a larger screen than an auto GPS, and they have lots of hard-drive storage for maps, but they aren't easily installed in your car, and they work best if you have either a copilot or software that gives audible directions. Otherwise, they are unsafe to use.

Experts say aftermarket GPS units are better and cheaper than those that come factory-installed in some new cars. The factory-installed units can't be updated and can only be used in one car. However, factory-installed GPS units do have two advantages: They offer a clean, integrated installation, and they are much more difficult to steal than aftermarket auto GPS units. This report covers aftermarket units; the factory-installed units are rarely reviewed.