"Don Tuite" wrote in message
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I am attempting to determine how the circle distances change as you
move from the equator to either of the poles.

r times two pi times the cosine of the latitude.

As a rough estimate, that's not bad. However, the Earth is not perfectly
spherical. It bulges out at the equator, and so you have to adjust r based
on latitude for that equation to come out right.

Pete