@whtemple1959
Are you just trying to transform OpenTTD to work on globe or are you trying to make the game to work with real 3D graphics?
If it is the first option than it can be done but you will have to lower the detail to only have roads and railroads between large cities. Reason for this is the fact that you will never manage to sucsesfully simulate everything if there would be too much detail.
I'm not sure for OpenTTD but original Transport Tycoon Delpuxe had the limitation of how mny of each structures, roadrs, rails can be on any map. And it was quite low so when playing on largest maps you quicly got to that limit which prevented you to build further.
This was all implemented so that game simulation kept running smothy even on bit weaker computers. I asume that OpenTTD has theese limits a lot higher since todays computers are much more powerfull. But still I don't think that they are enough powerfull of sucsessfully running simulation of the whole world with such detail as present in OpenTTD.
But if you plan on making your game in full 3D graphics than you will have to scale down your simulation part even further becouse processing 3D graphics is quite demanding.