Pontius Navigator,
I am not saying these are fir lines, as they do not match said lines from what people can tell.
But they indicate something, obviously, as they are clearly marked on this map. (I will search my history later and see if I can find the article I first grabbed the image from - although, I know for a fact it was in another language so not sure how helpful it will be even if I do manage to locate the article)
