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This symbol is on the tarmac at Ramona, CA airport. I've seen it at other small GA airports from Google Earth but I don't know what it is. Can someone please explain?

Ramona, CA airport

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up vote 33 down vote accepted

That is a Compass Rose, painted on a Compass Calibration Pad. It's used to mark a location on the airport surface that is suitable for calibrating the compass of an aircraft.

Here's one in a slightly different style:
Compass pad photo

and a more basic one from an FAA diagram:
Compass pad diagram

More information on the requirements for the compass rose / compass pad can be found in AC 150/5300-13, in Appendix 6.

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21  
Fun bonus fact: The compass rose in your photo was painted by The Ninety-Nines - they volunteer to do compass rose paintings at a lot of GA airports, and you can recognize their work by the 99s logo in the center of the compass rose. – voretaq7 Feb 8 at 20:08
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Related: Marking the way. – mins Feb 8 at 20:16
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@voretaq7 nice trivia. The 99s logo confused me because the runway is 9-27 and I thought it might be related to the runway heading. – PJNoes Feb 8 at 20:23
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Magnetic north drifts around fairly significantly - are these repainted on a regular basis? – meowsqueak Feb 9 at 3:36
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@meowsqueak Per the advisory circular: Magnetic surveys of existing compass calibration pads must be performed at regular intervals of 5 years or less. … Pads not resurveyed after 5 years or after nearby construction should not be used. - Whether this is actually done in practice varies, so it is prudent to check with the airport to determine the last time the compass pad was properly surveyed. – voretaq7 Feb 9 at 5:22

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