The Global Positioning Satellite system is the most important locating technology to be introduced to fishing since the introduction of the depthfinder. Its forerunner, Loran-C, deciphered your location by triangulating a series of signals from radio towers, signals that often were weakened or lost due to variations in weather.

GPS was developed for the U.S. Department of Defense, and its first widespread use was during the Gulf War. Drawing on a network of satellites orbiting some 11,000 miles above the earth, a GPS unit can triangulate locations for latitude and longitude to within 5 to 20 feet.

Not surprisingly, the number of anglers who own GPS units has skyrocketed. Prices have fallen and new technologies have appeared for both boat-mounted and handheld units. Many new sonar units also have GPS capability, and split-screen mode allows an angler to view bottom features and position simultaneously.

Anglers use GPS for better positioning accuracy, marking spots, mapping, and charting routes within water bodies. GPS mapping systems offer electronic displays of lakes, rivers, and their shorelines. In the mid-‘90s when GPS units first appeared on the scene, maps were cartridge-based and quite basic. They displayed freeway systems, state roads, midsized to large lakes and rivers, and medium to large towns. Background maps typically covered the entire U.S., as well as parts of Canada and Mexico. Greater topographic detail became available when manufacturers introduced cartridges or digital memory cards that enhanced designated areas on background maps. These provided additional useful navigational information— buoy markers, reefs, channels, and water depths. Extent and detail of coverage varies and certain computer applications are required, so check features before you buy electronic maps.

Mapping systems are available in chart-by-chart or seamless options. The chart-by-chart method is a digital version of the paper maps you’ve worked with for years, and it carries with it the same problem—differences of scale when you move from one map to another. The seamless method scrolls across a map with a uniform scale. The quality of mapping details is a function of two factors, the electronic file in the map cartridge and the acuity of your display monitor. In the case of a typical LCD screen, the total pixel count and the screen’s ability to react to light are the factors determining detail. Coarse screens may not adequately display all of the information available on a cartridge, particularly small details.

Keep in mind that zooming down to a small scale may not increase detail. It may mean instead that what you saw at 2 miles is only bigger at 0.2 mile, not more detailed. Different levels of detail should appear at different zoom or scale levels. For example, contour lines, small reefs, and islands that may not appear on a 20-mile scale should become visible on a 3-mile scale. Check to make sure that the mapping system you buy offers this capability.

The appearance of CD-ROMs in the GPS lineup means that instead of buying a handful of cartridges to cover all the areas you travel for outdoor activities, you can now cover the entire country in great detail with one or two CDs. When you load a mapping CD—such as Lowrance’s MapCreate or Garmin’s Road and Recreation and MetroGuide U.S.—the program appears on the monitor. Select or outline the area you want transferred to your GPS unit. The transfer is done through a data cable that attaches to the computer’s data port. Mapping programs allow you to create or customize your own maps, so you can choose the details you want displayed—small streams, rural roads, restaurants, street names, navigational aids, state parks, and so on.