 How to Calculate Magnetic Declination in Geography: First of all, let’s understand what Magnetic Declination is. The angle between magnetic north and true north is what called magnetic declination. Magnetic declination is also referred to as magnetic variation.

Magnetic declination ca also be understood as the Difference in degrees between True North and MAGNETIC North.

Did you know? By convention, declination is positive when magnetic north is east of true north, and negative when it is to the west. Isogonic lines are lines on the Earth’s surface along which the declination has the same constant value, and lines along which the declination is zero are called agonic lines. The lowercase Greek letter δ (delta) is frequently used as the symbol for magnetic declination.

## How to calculate magnetic bearing

Step 1: Determine the true bearing E.g 75°

Step 2: Determine the difference in years between the current year & the year
the Magnetic declination was measured (on topographic map). E.g. 2015 – 2005 = 10 years

Step 2: Calculate the total magnetic change
E.g 10 years x 2’ West = 20’ West (On the topographic map the change is 2’ West every year)

Step 3: Calculate the current magnetic declination
E.g 16°3’ West + 0°20’ West, When the mean annual change is west you add, & if the change is East, you subtract. = 16°23’ West Therefore, the magnetic declination for 2015 is 16°23’ west from True North.

Step 4: Calculate the magnetic bearing
E.g True Bearing + Current Magnetic Declination
= 75° + 16°23’
= 91°21’ west.

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