Wednesday, March 6, 2013

A tale of two...norths?

2011 7.5-minute Everett, WA topographic declination key
Odds are that anyone who has held a map in their hands has tried to make it point north.  But did you realize that there is more than one north?  Both "true north" and "magnetic north" are represented on a topographic map.  True north is the direction along the earth's surface towards the geographic north pole (indicated by the star in the image).  Magnetic north is the direction along the earth's surface towards the magnetic north pole (MN in the image).  In the margin of a topographic map there will be a small graphic
that depicts the difference between true and magnetic north.  This value will have to be added to or subtracted from your compass bearings for the best accuracy.  There are also other ways to compensate for this difference (declination).  Check out your Scout Handbook for procedures that involve drawing magnetic north lines on your map and for calibrating a declination-adjustible compass, if you have a compass with this feature.  Once you have a good sense of the difference between the "two norths" and how they relate to using your map and compass together you will not have to worry about following skewed bearings and getting lost due to poor accuracy.



Bonus: The declination key above is from the 2011 7.5' USGS Quadrangle for Everett.  You can view the map by clicking on the image (it may take a few moments to load).  You can then view the map in your browser or download it to your computer to explore the map features.  If you download the map use the zoom feature to find the "Scout Shack" and most importantly have fun!