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The Poles

An isogonic chart. Magnetic meridians are in black and
An isogonic chart. Magnetic meridians are in black and geographic meridians and parallels are in blue.

There are two types of poles on the Earth: two geographic poles and a magnetic pole. The geographic poles are located at the exact northern and southern-most points on the globe. The North Pole is at 90 N latitude, and the South Pole is at 90 S. All lines of latitude come together (or converge) at the north and south poles. This is also called true north and south.

A compass will point to the magnetic north pole. This is a point in northern Canada located close to 71 N latitude, 96 W that is about 1,300 miles (2,092 kilometers) from true north. It is where the Earth's magnetic pull is the strongest. The lines of force that lead to the magnetic pole are not straight like the lines that lead to the geographic poles but weave back and forth according to the magnetic fields in the Earth.

A typical isogonic chart
A typical isogonic chart. The black lines are isogonic lines that connect geographic points with identical magnetic variation. An agonic line depicts a point where there is no variation between true north and magnetic north.
When a pilot plots his course, he must allow for the difference between the degrees as shown on a compass and the degrees as shown on a geographic map. The angle between a magnetic and a geographic meridian (the lines of longitude) is called variation. For instance, if the variation is shown as 9 E, this means that magnetic north is 9 east of true north. The type of map or chart that connects the points with the same magnetic variation is called an isogonic chart.