NavList:

The video talks about surveying with magnetic compasses. I don't believe that this is correct. Surveying townships and all that was based almost exclusively on astronomical observations for baselines and standard ground-based techniques to fill in the details.

I didn't watch the whole video, but did it also suggest that compass needles were "spinning"? This is never real, but it seems to be a popular expression. If I am walking through territory with significant iron deposits, the magnetic field lines may well be pointing in directions that are locally inconsistent with expected variation/declination of the compass, but the field lines are locally constant. They don't spin, right? So what real phenomenon are people trying to describe, if any, when they talk about spinning compass needles?

Frank Reed