Just to add to this - I think the plan for the basic game is that the worlds are like Minecraft ones - ie generated by a seed, but infinitely large (or at least close enough to “infinitely large” that you’ll never reach the edge, which is good enough 
).
That said, a (Civ-style / side-scrolling) world map you can slap your hearthlings down onto, explore and such, with clearly defined boundaries, would be a great alternative mode IMHO.
I might also refer you to this old topic of mine, where I mentioned some of this 
: