How a GPS Works

Handheld GPS

The Global Positioning System (GPS) is made up of a network of 24 satellites that orbit the earth twice a day transmitting precise time and position information. With a handheld GPS receiver, you can determine your location anywhere on earth.
A GPS receiver works by listening to the signal of three or more satellites and, by measuring the time interval between the transmission and the reception of a satellite signal, calculates the distance between the user and the satellite. Using the distance measurements of at least three satellites and some fancy math footwork known as algorithms, the GPS establishes an accurate position fix. Three satellites must be acquired for the GPS to accurately display longitude and latitude, and four satellites must be acquired to add elevation to the mix.

The Pros and Cons

With a GPS, you can:

Determine your exact location on the map with a simple press of a button, even under cloud cover or dense fog
Enter a location from the map into memory; the GPS will help guide you there
Store information in the GPS as you travel so that it will help to guide you back

GPS performance is limited by:

High mountains
Deep canyons
Dense forests
Jungle canopy
The fact it requires battery power

Ask yourself: Without a GPS, could you determine where you are and how to head for home using just a map and compass? If your answer is anything less than a firm and emphatic "absolutely no problem," you need to acquire these skills — and soon.

Key Features, P.2 >>