Very interesting. Do I interpret this correctly that if one set out in 1590 from Norway towards magnetic North, one would end up in south America, via Iceland, and the go through the south pacific before turning (true) northerly again? How do we know that was the case?
@Cobalt, no, the lines on the map are not magnetic meridians but merely isogonic lines (lines of equal magnetic declination). Magnetic meridians are much less curvy.
