Engine is free, most data are not. See: https://te4.org/license
It is unclear to me if the worldmap and cities are FOSS or not from that description, after all, it is graphical stuff. And thus, it is unclear to me if the gamedata, outside of the graphics and sounds, are really FOSS. One can probably go read the code to know more though: if they can be found, then they might be FOSS, otherwise they're not.