Here is the long awaited GPS review. Now even though I work in the GIS (geographical information systems) and mapping field, I am not an expert on GPS. This report is based on what I have experienced using my own GPS and from reading articles about GPS and is solely my opinion. This is just a general overview of GPS. More detailed information can be found at http://gpsinformation.net/.

The problem with GPS units is that it gets complicated when you want or need one that is fairly accurate. The accuracy of the X and Y values (latitude and longitude) on consumer models can be anywhere from 10 feet to over 50 feet. And the elevation value (Z) will be at least 1.5 times less accurate than this. This is all because of satellite location. If the unit can’t see the satellites, then it can’t get a location. Reasons the unit can’t see a satellite could be that the satellite is too close to the horizon and is blocked from view or you are using it under heavy tree cover. Even tall buildings will block signals. And just forget using them in a narrow canyon. Even the survey grade units ($5000 and over) will run into the same problems. The way these become more accurate is by using known x, y, and z points with remote beacons and then taking the data and doing differential correction to the values. Plus, the units are big… you wouldn’t want to carry one around.

So, this brings us to the point of what to use. I’ve been using a Garmin GPSMap 76 for a couple of years now and have had good luck with it. It is actually listed as a marine unit and is totally waterproof and will float if dropped in water. When looking for one, I knew I wanted a unit that I could use for making maps. Now the unit itself won’t make the maps, but there is software that will. Some programs are free, some are not. The GPS Map 76 is not a small unit, but is fairly light. It is about the width of a deck of cards and about twice the length. I have carried it in my CamelBak while riding a bike and have recently started carrying it in my hand for running. This way I can keep an eye on my distance, moving time, stopped time, moving average speed, etc. The only problem with carrying it this way is that the unit needs to be vertical or close to it for the best accuracy, so your arm and hand will get a little tired. This isn’t as bad as it sounds though. But, I wouldn’t want to run with it in this manner for more than a few miles. I’ve also just purchased a mount for my bike handlebars and this works great. Like my own little dashboard of information. I tried running with it attached to my waist, but it loses signal too easily.

There are a couple of new units that Garmin makes that I would consider over the GPS Map76 and these are the Garmin Vista and the Garmin GPS Map76S with the Vista getting the nod due to its smaller size. Both of these units will do about the same as the Map76, but do have more memory. This translates into the ability to store more points. The Garmin eTrex series is also good and the perfect size, but you lose the ability to set the interval for collecting track points. I use this feature quite often on mine. A track log is a “bread crumb” trail of where you have been. The unit collects points at a certain interval – time or distance – and then basically connects the dots. On the eTrex series, you can’t adjust the collection interval. But on the GPS Map76, Map76S, and the Vista you can. The reason I want the capability to adjust this interval is that the units have a certain number of points they can collect. With the GPS Map76 this number is 2048. So, if I’m collecting points every 5 seconds then my total collecting time would be about 2 hours, 50 minutes. If I bump the time to every 3 seconds then this makes my total collecting time about 1 hour, 40 minutes. So as you can see, this could come into play if you plan on using the unit on a log hike, run, or bike. The bad thing about increasing the interval time is that you lose accuracy when downloading to the mapping software. For example, you are hiking along and the unit takes a point at the beginning of a turn or curve in the trail, then it doesn’t take another point until the end of the turn or curve. The resulting track will be a straight line from one point to the other. It will not show a curve. Remember, it is connecting the dots. So, the goal is to have a pretty close idea how long you will be using the unit to collect data and then adjust the interval accordingly. I have also found that collecting points by interval doesn’t work as well as by time.

This was a very quick overview and there is quite a bit more to using GPS units. To really explain and show what you can do with one is to go out and use it. I will write another article on some of the software that I have used to download the points from the GPS.

Chris Matus