GPS Setup - Map Datum

Map Datum is a critical GPS setting. In my land navigation classes I emphasize that hiking groups should all be on the “same page” regarding the set-up options of their GPS receivers. There are several essential steps that ensure accurate position reporting, rendezvousing and returning to camp safely. 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. Map datum is 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.  Receivers are set at the factory to WGS 84. To change the datum go to the receiver's main menu and select "set up" from there go to "position format."