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This seems quite silly, but I realize that I don't know the "official"
definition of a degree of latitude.

I'm sure most on this list know that the earth is an oblate spheroid --
it's fatter than it is tall.   This means if I cut the earth in half
through its poles, the resulting cross-section looks like an ellipse,
wider than it is tall, rather than a perfect circle.   And this
elliptical cross-section can lead to two possible definitions of a
degree of latitude.

If take a cross-section of the earth and draw an angle one degree up
from the equator, is the place where this line intersects the surface of
the earth the first (degree) parallel?   Or is the first parallel one
ninetieth of the way from the equator to the pole?

Years ago I took an offshore navigation course that taught the various
"sailings," including use of the Meridional Parts table from Bowditch to
determine a rhumb line course when traversing long distances (especially
those with dramatic north-south differences).   (Meridional Parts give
the "stretch" in the latitude scale required at various latitudes to
create a Mercator chart).   As I recollect, the meridional parts down
near the equator are actually slightly less than 1.00000, which would
indicate that the first of my two definitions is the correct one.

I know there are some experts in cartography on the list, I'm sure this
is trivial for them.

Lu Abel

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