Map Datum

For most hikers, the map datum selection isn't critical.  New and right out of the box, GPS receivers are set to Map Datum WGS84. And for most hikers that setting will be just fine. Out and back - no problem. But if you are going to take coordinates taken from a map or from a friend, AND accuracy is important, ensure you use the right map datum. Map Datum is defined as: "A mathematical model of the Earth used by map makers.  Datum allows for the accurate transfer of geographic data from a spherical earth to a flat map.  In the United States, there are three common map datum’s found on topographic maps.  These are WGS 84, North American Datum 1927 (NAD27) and NAD83.  Select the datum that is used on the map. "   Not selecting the correct map datum could induce an error of over 100 meters/yards. I emphasize that hiking groups should all be on the “same page” regarding the set-up options of their GPS receivers.  Map Datum information is found in the map key on most maps.   While planning a journey or at the trail head, taking the time to adjust settings among hiking partners is critical.  Before departing, validating map datum and coordinate format should be a priority. First, match the map’s datum.  A topographic map identifies datum in the map key.  Once the datum is identified ensure that all GPS receivers are set to match the correct datum.  See the illustration below. For more information on GPS setup setting check out: Improving GPS Accuracy, Setup Your GPS