In North America, a line with zero declination runs roughly from west of Hudson Bay down along eastern Lake Michigan to the Gulf of Mexico in Alabama (see declination map above).  The declination lines pictured in the map above move slightly to the west on an annual basis.  So, it is important to look at a current isogonic (declination) map to know the correct declination in your area.

At any point on the west side of the zero declination line, the compass needle will point east of True North.  This is called "easterly declination".  At any point east of the zero declination line, the compass needle will point west of True North.  This is called "westerly declination".  In North America, magnetic declination varies from 30° east in Alaska to 30° west in Labrador.

The Magnetic North line (and the resulting declination angle) in Photo 1 (see previous page) points to the left (west) of the True North line.  Therefore, any location on this specific topographic map would have westerly declination.  To correct the bearing of the Point A-B line on the topographic map for declination, the declination shown in Photo 1 is added to the bearing.

There is a simple saying that makes declination determination easy to remember…east (declination) is least (subtract) and west (declination) is best (add).