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Old 10-04-2012
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Re: Great Lakes Boaters, Polyconic charts, mph

Originally Posted by Hartley18 View Post
Righto.. What's this then?? Looks like nautical miles (and tenths) to me:

Attachment 12380

I understand that the Polyconic nature of the chart means that lines of lattitude and longtitude aren't necessarily straight up that part of the world, but don't get me wrong, I'm happy to learn something new.
It is the latitude scale, used to measure distance on a Mercator projection.

Polyconic projections are common in the Great Lakes of Canada and the US.
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