Map, Compass & GPS

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

Monday, December 2, 2013

GPS Setup - North or Magnetic North

Should you use true north or magnetic north when you setup your GPS receiver?
I keep my navigation simple and choose true north.

GPS receivers provide an amazing amount of information. They come loaded with many navigation features, maps, tide data and much more, but nothing is more important than position data and the direction to a waypoint.

Much of land navigation is based on the relationship to the North Pole; also known as “true north.  The measure of degrees of direction in relation to true north is called “degrees true.”   Maps are laid out in degrees true.  Land features (buttes, mountains, streams) on a topographic map are in reference to degrees true.  By that I mean the bearing from one mountain peak to another will be referenced in degrees true.  

The issue is that the magnetic compass’s direction information is in degrees magnetic.  The angular measurement between degrees true and degrees magnetic is called declination.   The hiker will need to compensate for declination.

In the Navy I learned to keep my navigation simple.

In the Navy during a bridge watch, I evaluated the ship’s position on a navigation chart.  The principle navigation compass (a gyro repeater) reported in degrees true; the backup compass reported in degrees magnetic.    Key to this navigation was the both the principle navigation compass and chart used degrees true.
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