How to compensate for magnetic declination when reading a compass. In this example, the declination is 14°E (+14°), so the compass card points to a north 14 degrees to the East of true North. To obtain a true bearing, add 14 degrees to the bearing shown by the compass.
https://en.wikipedia.org/wiki/Magnetic_declination
Magnetic declination or variation is the angle on the horizontal plane between magnetic north (the direction the north end of a compass needle points, corresponding to the direction of the Earth's magnetic field lines) and true north (the direction along a meridian towards the geographic North Pole).
https://en.wikipedia.org/wiki/Magnetic_declination
Wrong. To get to the North Pole, or true north, just following your compass needle won't work. If you want to get from a point at the bottom of a map to one at the top, you need to head true north. True north is a geographical direction represented on maps and globes by lines of longitude.
http://adventure.howstuffworks.com/survival/wilderness/true-north.htm
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.
https://en.wikipedia.org/wiki/Magnetic_declination
The Earth is one big magnet. The Magnetic North Pole (also known as the North Dip Pole) is a point on Ellesmere Island in Northern Canada where the northern lines of attraction enter the Earth. A compass needle rests freely in its casing so it can maneuver itself.
http://gisgeography.com/magnetic-north-vs-geographic-true-pole/
This angle varies depending on position on the Earth's surface, and changes over time. Somewhat more formally, Bowditch defines variation as “the angle between the magnetic and geographic meridians at any place, expressed in degrees and minutes east or west to indicate the direction of magnetic north from true north.
https://en.wikipedia.org/wiki/Magnetic_declination
In the northern hemisphere, declination can therefore be approximately determined as the difference between the magnetic bearing and a visual bearing on Polaris. Polaris currently traces a circle 0.75° in radius around the north celestial pole, so this technique is accurate to within a degree.
https://en.wikipedia.org/wiki/Magnetic_declination
This is a difference of about 500 kilometers between the Geographic North and Magnetic North poles! This difference is called the magnetic inclination. Magnetic deviation is the error of a compass needle including nearby metallic objects. Magnetic inclination varies according to where you are located on the globe.
http://gisgeography.com/magnetic-north-vs-geographic-true-pole/
The Magnetic Pole is a point in Northern Canada where the northern lines of attraction enter the Earth. A compass needle will point to the direction of the Magnetic North Pole. But this doesn’t mean that a compass always points to the Geographic North Pole. This difference is magnetic inclination.
http://gisgeography.com/magnetic-north-vs-geographic-true-pole/
For that reason, there is a difference between true north on a map and the north indicated by your compass. That difference is called the magnetic declination and is measured by the angle between true north and magnetic north when plotted on a map. Magnetic declinations vary from place to place, depending on the intensity of the Earth's magnetic fields. For instance, if you hold out a compass in New Zealand, magnetic north will be about 20 degrees east of true north, whereas the declination in Los Angeles is 12 degrees.
http://adventure.howstuffworks.com/survival/wilderness/true-north.htm
what term applies to the difference between true north and magnetic north
The term Intensity of the Earth's magnetic fields applies to the difference between true north and magnetic north. Intensity of the Earth's magnetic field applies to the difference between true north and magnetic north.