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    Re: What is a degree of latitude?
    From: Richard B. Langley
    Date: 2008 Mar 23, 16:23 -0300

    You might be talking about the difference between geodetic (or ellipsoidal)
    latitude and geocentric latitude. Have a look at the figure on this page
     to see if it helps.
    -- Richard Langley
       Professor of Geodesy and Precision Navigation
    
    On Sun, 23 Mar 2008, Lu Abel wrote:
    
    >
    >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
    >
    >>
    >
    
    
    ===============================================================================
     Richard B. Langley                            E-mail: lang---.ca
     Geodetic Research Laboratory                  Web: http://www.unb.ca/GGE/
     Dept. of Geodesy and Geomatics Engineering    Phone:    +1 506 453-5142
     University of New Brunswick                   Fax:      +1 506 453-4943
     Fredericton, N.B., Canada  E3B 5A3
         Fredericton?  Where's that?  See: http://www.city.fredericton.nb.ca/
    ===============================================================================
    
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