Boy Scout Troop 127
Backpacking Tip 33
Orientate a Map
Orienting a map is the starting point for any map work.
After orienting the map you can identify where you are,
where you want to go and where you have been.
Use a US Geologic Survey (USGS) map at the scale of the
1:24,000. This is a 7.5-minute topographic map.
Find the declination diagram in the map's margin. This is
usually at the bottom of the map. It looks like a little V and
tells you the difference between magnetic north (where a
compass needle points) and map north (the top of the map).
The difference between the angles is called magnetic
declination, and it varies from 21 degrees west in Maine to
26 degrees east in Alaska. Phoenix is about 12 degrees
East. I recommend using your home computer to verify the
map declination information at:
www.magnetic-declination.com.
One of the better ways to "defeat" declination problems is
to draw magnetic north lines on the map at one inch
intervals. Do not, repeat, DO NOT, try to use the diagram
arrow at the bottom of the map. It isn't long enough to give
a reliable line.
At Home Depot I brought the “Original True Angle” by
Quint Measuring Systems. This is a 21-inch long
protractor. It is easy to set the angle. Use this to draw
declination lines on the map.
Put the compass body along one of the drawn declination
lines and rotate the map until the “red is in the shed”. Now
the map is pointing to magnetic North.