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. Each line of longitude begins and ends at the Earth's poles and represents direct north and south travel.
Compasses, on the other hand, direct you to magnetic north, a point in the arctic regions of Canada that continually shifts location based on the activity of the Earth's magnetic fields. Fluid iron in the planet's core acts like a huge bar magnet, creating a relatively weak magnetic field. The force of that magnetic field has a horizontal component in the direction of magnetic north. A compass needle is magnetized and freely suspended to allow that horizontal force to pull it toward magnetic north as well.
But the Earth's magnet isn't perfectly aligned with the geographical poles. 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. Geographical lines do exist where true north and magnetic north are aligned, and these are called agonic lines. In North America, one currently runs through the panhandle of Florida up to the Great Lakes and into the Arctic Ocean.
Given these irregularities, how will you ever reach the North Pole or a true north destination? Read on to find out how you can do it -- any time of day and with man-made and natural navigation tools.
http://adventure.howstuffworks.com/survival/wilderness/true-north.htm
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