A follow-up from this question; one of the answers mentioned that the compass rose in the picture was used to calibrate an aircraft's compass.
But how does that actually work? Do you park the aircraft on top or something?
Most aircraft compasses include compensating magnets to correct for installation error (due to natural magnetic fields in an aircraft from steel parts and electrical equipment). When installing a new compass or performing significant electrical work on an aircraft the compass may need to be re-calibrated and the compensating magnets adjusted (typically by turning small screws, like the ones shown below).
There are several ways to calibrate (or "swing") an aircraft compass - the use of a properly-surveyed compass rose constructed to applicable FAA standards and marked on an airport is one of them, and ensures the compass swing is being performed in an area free of magnetic disturbances which should result in an accurate calibration.
The basic procedure is to taxi the aircraft to the compass rose and align it with the compass directions using a combination of the ground markings and a "gunsight" compass. A full description of the procedure can be found in AC 43-13.1, Chapter 12-37 ("Compass Swing"), but the quick-and-dirty version is:
Once the compensating magnets have been adjusted a Compass Deviation Card is prepared to inform the pilot of the remaining compass error.
Beginning with Magnetic West (270) turn the aircraft to align with each of the 30-degree lines on the compass rose (270, 300, 330, North, 30, 60, 90, 120, 150, 180, 210, 240), and the error is recorded on a compass deviation card similar to the one shown below.
A compass reading within ±10 degrees on each 30-degree heading marker is considered acceptable per AC 43-13, and better results are usually achieved.
The compass swing is typically performed with the engine and electrical accessories (radios) running per AC 43-13. Some mechanics may also perform a second swing with radios off, and include an alternate deviation card for that configuration.
A clever way to alight the aircraft is to put both wheels on the desired radial line that is orthogonal to the desired heading. For example, if you put both main landing gear exactly on the 270 radial line with the right wheel on the inner part of the radial circle, then your aircraft is pointing north (orthogonal to the 27 radial line). You can repeat this procedure for each radial line to get the desired heading. This works particularly well for a high wing aircraft such as a 182. For a low wing aircraft you could use a spotter outside the aircraft to help determine when wheels are on the line.