Map, Compass & GPS

Map, Compass & GPS
Wild flowers along Fall Creek on the way to the Green Lakes - Oregon

Thursday, December 20, 2012

GPS Setup

Before heading out into the back country, spend a few minutes to update the settings on your GPS receiver.

Setup is a straight forward process that everyone in the hiking party should do.  Everyone should be on the same page.  For example, if the hiker is to meet at a spot for lunch, wouldn't it be nice if all met at exactly the right spot?  If receiver settings don't match the group may be over a hundred yards apart from each other.

So, here is what I recommend.

  • First, remember the prhase, "match the map."  The receivers all need to match the parameters of the map.
  • Geographic coordinates:  This is the grid system on the map.  Most commonly the grid can be either Latitude/Longitude or UTM grid.  Keep in mind that Latitude and Longitude settings in your receiver and set at the the factory are Degrees Minutes.Minutes.  The map is set to Degrees Minutes Seconds.  They are close but not the same.  To adjust these receivers settings settings (for a Garmin 60 series), select main menu, then select setup, then units.  Check your owner's manual.  Personally, I use UTM grid.  UTM = Universal Transverse Mercator.  It's a much simpler grid system to use.  For information on how to use UTM go to the USGS site here.
  • Map Datum:  On USGS topo maps and most Forest Service maps, map datum is listed in the  bottom left corner of the map.  It might indicate that the horizontal datum is North American Datum 1927 or North American Datum 1983.  To match the map go back to receiver setup and select units.  Norht American Datum 1927 will be listed by the acronym NAD27 CONUS (for Continental United States).  That is the option you want.
         The web site has a nice description of Map Datum here.

  • I always recommend the hiker carry a declination adjustable compass.  Visit the website to find the correct declination for the area you will be hiking in.  The compass will now provide data in degrees true.  Now adjust the GPS receiver via the setup function again, and select "heading".  Then selction the option "True."  Now the hiker will match the map and the compass.
Note that older USGS topographic maps may have declination data that is very old.  Do not rely on that information.

If everyone in your party "matches the map" you all will be on the same page and this greatly simplifies a rendezvous and  keeps your navigation simple.

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