Using GPS Device

Should I use my GPS to navigate to the hut? 

We advise against relying solely only on the GPS for use in accessing the huts because they may not provide the desired accuracy due to weak satellite signals caused by forest cover, inclement weather, topography, less-than-ideal satellite positions, and other factors. A GPS unit can be a good tool for backcountry navigation when used in conjunction with a map, compass, altimeter and appropriate skills.  If your GPS fails, you will be very thankful that you wisely brought your map, compass, and altimeter - and know how to use them.

What is a mapping datum?

A datum is a mathematical model of the Earth which approximates the shape of the Earth and is used as a reference on maps. It enables calculations such as position and area to be carried out in a consistent and accurate manner even though the earth is not perfectly round, but is spheroid in shape.  Every map has a map datum reference that is usually listed in the title block or legend of the map.

Why do I need to know about mapping datums and which one should I use?

When using a map and GPS together for navigation, your GPS must be set to the same datum as the map you are using. Failure to do so could result in errors of 200 meters or more in your displayed position.  This is because the same position on earth (a hut or trailhead for example) will have different coordinates depending on the datum used to create the map.    Most United States Geological Survey (USGS) topographic maps and ALL 10th Mountain Division Hut Association winter maps are referenced using NAD 27.  Some newer USGS maps use NAD 83. If you are using your GPS without a map (shame on you for not having a map!), using WGS84 is generally the best datum to use as it is considered the most accurate datum to use with a GPS alone. Consult your GPS owner’s manual to learn how to set the correct datum to match your map's datum.

Why are there two mapping datums? Over the years, many different datums have been developed and used as references on maps all over the world.  NAD27 (1927 North American Datum) and WGS84 (World Geodetic System 1984) are the two most predominantly used today.

REMEMBER! when using a map AND GPS together, BE SURE YOUR GPS IS SET TO THE SAME DATUM AS YOUR TOPO MAP!  Failure to do so could result in errors of 200 meters or more in your displayed position.  Consult your GPS owners manual to learn how to set the correct datum to match your map's datum.  Note that most GPS units come from the factory with WGS84 as the default map datum.

GPS coordinates in this site are carefully verified and tested, but are not guaranteed as 100% accurate. Before using any GPS coordinates from any source, always cross-check with a map to verify as closely as the map scale and Datum allows since a typo can result in a useless or possibly dangerous coordinate being entered into your GPS unit and used as a navigation goal. Coordinates in the charts are subject to revision as each location is re-checked using best available technology. Trailhead locations may vary due to snow plowing and road closures.   

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