This year, GPS navigation units will top many Christmas wish lists. Global Positioning System units are ideal for heavy travelers, commuters and those who get lost easily.

GPS units have chips that receive signals from satellites. The units use those to determine your coordinates and plot your position on a map.

There are various types of GPS units. Some are designed for hikers or boaters, but most people want a trip GPS to help navigate cities and highways.

MORE THAN MAPS

GPS manufacturers are including more features to help you in unfamiliar places. Some play MP3s, videos and pictures. Don't worry about these things.

Instead, focus on navigation abilities.

You want one that lists points of interest and maps alternate routes. You should be able to find nearby businesses by name or category. Alternate routes are handy, too. Some even help you avoid toll roads.

Some GPS devices provide turn-by-turn voice directions so that looking at the screen won't distract you. Make sure the unit includes both street names and distances in the directions.

REAL-TIME TRAFFIC

Commuters will love real-time traffic information. GPS units that can provide this data will show traffic flow and any tie-ups. They may also suggest alternate routes.

However, not all units provide traffic information and some require that you buy a traffic receiver separately. Traffic information may not be available in your area, and if it is, there will probably be a charge for it. Expect to pay about $50 or more a year for the service. But lifetime plans can save you a bundle.

Take this into consideration before you buy.

GARMIN NUVI 660

The Nuvi 660, which lists for more than $700 but, like all of the GPS models mentioned here, can be found for much less, features a large 4.3-inch screen. It connects to a car stereo via a built-in FM transmitter. It can play MP3s and give voice prompts. It also includes a traffic receiver.

The Nuvi 660 includes maps of the U.S. and Canada. The database includes almost 6 million points of interest.

TOMTOM GO 920 T

TomTom's GO 920 T ($700) also features a 4.3-inch screen and FM transmitter. You can play MP3s and record your own navigation instructions. There's also a traffic receiver.

TomTom says this unit's maps are the most extensive in its product lineup. Additionally, Map Share technology lets you update and personalize maps. Maps can also be shared with other users.

But what really sets this GPS device apart from others is voice-prompted address entry, which allows you to simply speak the address you want to travel to and the device automatically calculates the route.

MAGELLAN MAESTRO 3250

Magellan's Maestro 3250 ($400) has a smaller screen than the others at 3.5 inches. It provides voice directions and accepts voice commands. It includes a traffic receiver.

The maps cover the United States and Canada. There are 6 million points of interest in the database. It also provides AAA TourBook information.

FINAL CONSIDERATIONS

Before you buy a unit, test it. Make sure the screen is large enough, with a wide viewing angle. The controls should be easy to use, so the device won't be too distracting to drivers.

GPS units are attractive targets for thieves. Don't leave them unattended in your car. You could even end up with a broken window if you leave the devices in the windshield or dashboard mount.

The maps also must be updated periodically to include newer roads and points of interest. Don't get sticker shock! Maps can run hundreds of dollars.

Contact Kim Komando at gnstech@gns.gannett.com.