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GPS And Moving Maps

Posted in How To on November 1, 1998
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The increasing popularity of GPS receivers continues to be a source of amusement. People are so eager to show off their latest and greatest GPS receiver and all of its functions, but so few people show off what is really required to tap into the devices' usefulness; GPS receivers are only a small part of a navigation system.

Preparation is a big part of moving map software. At a minimum, a scanner and a good collection of topographic (topo) maps will get you started. Eventually the United States Geological Survey (USGS) DRG CD-ROMs may become a preferable alternative.

Maps continue to be the basis of navigation, and few people pull out their maps while showing off their GPS receivers. If they did, what at one time seemed so powerful and convenient would become arduous and time consuming-transferring the data back and forth between the map and the GPS. As such, other equipment becomes necessary: map interpolators, or rulers and calculators.

These requirements become apparent when you actually try to locate a new road in a place you've never been. All too often the topographic (topo) maps don't have more recent roads listed, or the roads on the map aren't readily found. Either way, the map and GPS receiver are linked together in the process of finding these locations. They are inseparable. Apparently, few people have used their GPS receiver to find a new place, because if they had, they'd find out what a pain it is.

Finding the exact values of a point on a topo map is easy, as long as you consider pulling over, taking out the map, and using a map interpolator or ruler and calculator to figure out these points. It's not something you do on-the-fly. Some GPS receivers, such as the Trimble Scoutmaster, do provide an "over-and-up" function to locate points in inches on a topo map, but you'll still have to use your ruler, thus wasting time. This process can be fatiguing when done all day long.

The technology exists to make this process effortless with moving map software, a laptop computer, and a scanner. Even an inexpensive monochrome computer is quite acceptable, and possibly preferable, as a laptop could lead a rough-and-dirty life used this way. The scanner is only needed at home. If you use a more modern laptop with CD-ROM drive, you can use the United States Geological Survey (USGS) DRG CD-ROMs, which contain 64 maps per CD-ROM.

When you use the software on the trail the value becomes awesome! There's nothing like being able to stare down at a screen that shows a real topo map and a cursor on the map representing your position. Not enough can be said to convey the navigational power of this equipment. It's certainly worth any wear and tear the laptop may see. For that matter, even if you don't use the moving map, the software simplifies point plotting.

In order to accomplish full moving map capability, a GPS receiver with an NMEA RS-232 output is required. The output simply plugs into the serial port of the laptop. Most midrange-up GPS receivers offer this capability, and usually require purchasing an optional cable.

Several sources are available for moving map software including (as well as several shareware sites on the Internet): and

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