Old Stone Walls Reveal How Earth’s Magnetic North Changes over Time

The difference in direction between true north and magnetic north (at a specific time and location on the Earth) is known as the magnetic declination. But now my work on 726 miles of stone walls provides an independent check on magnetic declination between 1685 and 1910. Using LiDAR images, the bearings of those stone walls could be determined with respect to true north and compared with the surveyors’ magnetic bearings.

Source: www.citylab.com