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Many old maps have lines like below. Is there a term for a map with that type of lines? enter image description here enter image description here (from

My best hypothesis is that the lines may be related to Rhumb lines and therefore Mercator projections.

Beautiful Example.

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I think this is an example of a question that can correctly exist on 2 different SE sites--you might consider posting this question on with a cartography and history tag. There are lots of good cartographers there. –  Jay Aug 13 '12 at 9:56
I don't understand "pin-wheels" here. What is this supposed to mean ? –  Nicolas Barbulesco Aug 29 '14 at 12:16

1 Answer 1

up vote 5 down vote accepted

The first thing I can think of is Portolan charts, the Wikipedia page is not very clear but it links here which has some more information. (full frameset for the second link)

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+1. I think it would make this answer more valuable though if you'd quote their paragraph on what the lines were for. That was the main thrust of the question. –  T.E.D. Aug 13 '12 at 13:55
@T.E.D. That paragraph essentially says, "yep, they're Rhumb lines for each of the primary, half-, and quarter-winds in Mercator projections", confirming JoeHobbit's suspicions. –  SevenSidedDie Aug 13 '12 at 17:27

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