–By Joe Stoddard

Thanks to the Defense Department, we civilians have free access to the Global Positioning System (GPS), also known as Navstar. GPS is a network of 24 satellites, 11,000 miles up and orbiting the Earth about twice daily. By latching on to any three of them at the same time, a GPS receiver can calculate its location anywhere. Add a fourth connection, and it can calculate its position in 3D space.

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Nuvi 750–Garmin International

Clearly, GPS is a boon for contractors of all sizes. In fact, in one Tools of the Trade survey conducted for this article, nearly all GPS owners recommended the technology. Some respondents already are using advanced, GPS-enhanced Terrestrial Positioning Systems, or TPS, for complex surveying, layout, and even takeoff and estimating.

Tools of the Trade sought to find how a typical contractor might use an off-the-shelf GPS device costing less than $600. Turns out, that's not much of a limitation: at $600 and under, there is a mind-boggling array of GPS products available, divided roughly into five categories.

Handheld receivers are intended primarily for outdoorsmen. Handhelds are used to mark a hiking route or favorite fishing spot, or play geocaching, a real-world treasure hunt game. Handhelds are more about walking (point-to-point navigation) than driving (turn-by-turn navigation), but you can find hybrids that will get you through a weekend in the Rockies and a work week in your Sierra.

Vehicle-oriented personal navigation devices or personal travel assistants are what most people think of as GPS. They are used primarily to get turn-by-turn driving directions and find pre-programmed points of interest, such as gas stations, hotels, and restaurants. Unfortunately, even though many are shirt-pocket portable, they usually lack the pedestrian/walking features found in handheld GPS receivers.

Every major U.S. cell phone carrier now offers GPS services and phones with GPS features. Typically, you'll pay about $10 a month (for Verizon and Sprint) for consumer service, and $20 to $25 a month for commercial and tracking capability; that's on top of a required data plan. A cell phone with GPS can be a great alternative to a dedicated device. It does as good a job with driving directions, and since it can get real-time information from the cellular network, traffic alerts and points of interest can be updated continuously. These devices also let contractors take advantage of lower-cost fleet-tracking services.

There are GPS kits and laptop and PDA add-ons that turn your laptop or PDA into a GPS device by plugging in an inexpensive receiver and running companion mapping software. Unfortunately, these kits have a reputation of being toys, not tools. They're slow, inaccurate, and generally inferior to dedicated GPS devices. But keep in mind you get what you pay for. If you want to spend $50, you'll get a toy, but there are professional-grade laptop and PDA receivers starting at around $150 to 200. Why not just buy a standalone unit? Add-on receivers make sense if you need more specialized software, such as a fleet-tracking applications that will show your driver the location of all your other drivers on a map.

Last, and probably least for contractors, are specialty devices. Most major manufacturers also produce GPS units specifically for aviation, marine and boating, motorcycling, sports, and other activities.