The Google Earth measurement would be fairly close (error of plus or minus 10 feet compared with line of sight surveying) -- and the calculations of the "surface of the sphere" don't apply here since the curvature of the Earth over a distance of 9 miles (which you can work out for yourself) is less than .01 inches.

If you want the exact measurement from the exact points, the easier way to get that data would probably be to spend the money and sign up with one of the large map/topo map providers on the Internet.


-- Byrd
Moderator, Hall of Ma'at