3D dynamic map generation

Hi guys,

I'm currently working on a small strategy game that involves online multiplayer. I was now planning to add a sort of 'Empire' map to my game. That is, a (3D?) map of different lands, similar to this:

Would there be any way to dynamically define and color land masses on a static, already-defined 3D terrain, similar to what the image above represents (it's a screenshot from Europa Universalis)? The data would be provided in .json format from an API backend - how should that data (for the dimensions of 'lands', or the countries) also be structured? I was thinking something along generating a .svg map, as seen here, but just in 3D.

I'm not asking for any code, just for ideas on how something like that could be dynamically achieved.

Thanks!