FOSS gamedev and creative worlds

So I plan to make a, Real Earth like world.
Before do so is, there any MG made to do so before my long work.

And before list ideas mods using etc.

well, I know for manually terraforming, worldedit is pretty nice.

might want to look into lua mapgen manip too

edit: fixed a misspelling

If you are talking about a 1:1 scale earth, it's not possible. The maximum mapgen is too small.