Find the correct declination for anywhere
Short answer: magnetic-declination.com. This brings up a Google map of the world, and one click gives you a pop-up box with the correct declination.
Long answer: Magnetic declination changes depending on where you are on the earth. It also changes in the same position over time, because the magnetic poles are moving.
Here’s a map showing how magnetic north has changed over the last 150 years or so.
image: geology.utah.gov
And here's a little chart showing how declination has changed in the Portland Oregon area over the last century or so. If you bought a map that was printed around 1980, the declination would be incorrect for the current day.
Below is a world map of declination. (Red lines = east declination, Blue lines = west declination, Green lines = zero declination). (The lines look so whacky because cartographers are trying to represent the 3D curved magnetic flux lines of the earth on a flat 2D surface)
Zero declination or close to it, is in the central USA, northern Africa, India, China, and most of central Europe. Here, your compass pretty much points to magnetic north AND true north, lucky you.
The closer you get to the magnetic poles, the crazier the declination. You can see why polar explorers have an extra challenge - compasses basically don’t work.
source: geokov.com
So . . . I just want to set my compass declination to my local area- how do I do that?
Your map may not help. As you can see from the top image, declination has changed fast in the last 2 decades. A value that might be printed on the margin of a map may well be out of date, especially if the map is more than 10 or 20 years old.
Good news: it's easy to find the current and correct declination for any place on earth.
Just go to:
magnetic-declination.com
This brings up a Google map of the world, and one click gives you a pop-up box with the correct declination.
It's fun to click around in places that have some pretty crazy declination, such as New Zealand and up in northern Alaska and Canada.
Click around south of Australia in Antarctica, and see why compasses are often useless for polar explorers - near the northern and southern magnetic poles, compasses start doing some pretty crazy things!
Note:
“positive” declination = east declination, such as in Oregon
“negative” declination = west declination, such as in Vermont
If you want to learn more about declination, what it is, how to deal with this, and when you do and do not need to care about it, check out this Youtube video from the Columbia River Orienteering Club.
