=> New to MFD9...measurement problems (georeference.org)
=> Geom SQL Functions (manifold.net)
GeomLengthGeo(<geom>, <major>, <eccentricity>, <tolerance>): <value>
Given a geom that contains an area or a line object, and values for major axis, eccentricity, and tolerance, returns the geodetic length (computed on the surface of the ellipsoid) of that object, computed using Vincenty's formulae A tolerance of zero means automatic tolerance.
The length of an area object is the length of its boundary, that is, the perimeter of the area. The length reported for a branched object is the sum of the lengths of the branches.
The geom value must be an area or line in Latitude / Longitude, with X (longitude) and Y (latitude) expressed in degrees. The returned value is in units of the major axis.
Looking at the Custom tab of the Base Coordinate System dialog for the WGS84 base used for Latitude / Longitude projection, we can see the major axis is 6378137.01 and the eccentricity is 0.08181919084262149
Given a Mexico drawing of provinces as areas in Latitude / Longitude coordinate system, we can write:
SELECT GeomLengthGeo([Geom], 6378137.01, 0.08181919084262149, 0) AS [Geodetic Length] FROM [Mexico];
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