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

Originally Posted by Hartley18 View Post
So, as a Yachtmaster Instructor, you're telling me that the bit I circled doesn't represent a distance of ten nautical miles??

From wonderful wikipedia: "The nautical mile (symbol M, NM or nmi) is a unit of length that is about one minute of arc of latitude measured along any meridian... By international agreement it is 1,852 metres (approximately 6,076 feet)."

Perhaps it's a good thing I'll never have to sail in that part of the world.
That works well on a Mercator projection. On a polyconic chart the distance is distorted as you move away from the central meridian.

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