Jan,
Thanks for your thoughts. As far as ADE, I just use it with an ortho-rectified aerial image from FsEarthTiles so I know the lat/lon corners, and then lay out the runways and taxiways over the real image - and save that - no hangars, no aircraft,etc. Then I use Flight1 Instant Scenery 3 to select library objects (including ones that I have added - aircraft, buildings, trees, cars, towers, ILS shacks,etc...) and move them carefully into place using the realtime FSX/P3D screen to see that they are going to the exact spot and orientation I want - which then updates the placement BGL file. I can fly right then without having to restart and test, restart and test! One to two hours later, I have a pretty good airport - assuming that a flat rectangular area is OK. If I need some different elevations, then SbuilderX is utilized to fiddle with terrain height. Instant Scenery 3 is $30 - wonderful - the other tools are freeware - BTW, add ModelConverterX from fsdeveloper.com into the mix in order to view and fixup the actual objects.
@IPACS - I now get the correct answers for lonlat to web-mercator conversion at Kingman - BUT not exactly, either my trig functions are different (I'm using Visual Studio 2015 with everything being "double" ) or my values for PI and TM_PI and Rad_to_Degree are slightly different - if you could provide those, it would be helpful. Again, thanks for the code - pretty much what I had but different scale factors. I now can place some objects at KOKB - my home airport in Oceanside, CA. Thanks again!