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Why is this compass considerably off?

Geographic Information Systems Asked by Cotton Headed Ninnymuggins on December 25, 2020

Here is a Google Earth screenshot of “Edwards AFB” in California:
enter image description here

-The green circle has the compass in it…

Here’s a zoomed in screenshot of the compass:
enter image description here

Notice how my Google Earth compass (in green again) is pointing directly North but the compass in the picture isn’t very close to pointing North compared to the other one

If I had to guess which compass is off, I would say it’s Google’s, but why wouldn’t the compasses be closer than this?

One Answer

Google Earth's compass points towards the geographic North Pole, while airplanes traditionnally work with magnetic compasses, hence all compasses and airstrip numbers are relative to the Earth's North Magnetic Pole (they use the magnetic field). The compass that you see in the sand at Edwards AFB is a magnetic compass, pointing towards the North Magnetic Pole, and is offset by around 15° from geographic bearings. The difference between the two is call the magnetic declination.

Correct answer by FSimardGIS on December 25, 2020

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