JLWest is worried about a distance in the calculation by 41 km. I have no idea what he is doing, maybe incorrect conversion between miles and kilometers. I only wanted to point to the error source due to the elliptical shape of the earth. Since I do not have any idea how many km this would be I used the distance calculation from LazMapViewer (which is based on a spherical shape) and that of

https://forum.lazarus.freepascal.org/index.php/topic,46737.msg333796.html#msg333796 (whch is based on an elliptical shape) and calculated the distance between the geo locations mentioned further up in the text:

- spherical surface: 9251 km

- elliptical surface: 9264 km

A difference of 13 km. The same order of magnitude observed by JLWest, but only a third of the value. Therefore his error must be somewhere else.

My question about the "official" handling of distance calculation: i picked another example: a flight from Munich (MUC) to San Francisco (SFO). According to

https://www.airmilescalculator.com/distance/muc-to-sfo/ the flight distance is 9461 km. The calculation with the spherical surface yields 9448 km, the elliptical surface 9461 km - exactly the result of the airmilecalculator. Therefore, I'd conclude that flight distances are calculated based on the elliptical shape of out planet.