Is it possible to play on a single-region map?

[Keeper Of Insanity]

I know it's against the game's concept, but I find it boring to develop every new region from scratch and think that it's artificially extended.

So, if possible, I would prefer to build a single city with all available resources and be able to explore the entire skill tree.

[Martin]

Via the trade system you essentially can do this. Once over 1000 citizens the game becomes unstable tho. Depending on your hardware, you might have issues over 650 or so. Spreading this out over several towns should reduce the instability.. maybe at a later stage of development this might be possible to have single region maps.

[Brodaty]

Not yet.
But you can import all resources from small self-sustaining villages. You can't unlock all stuff in one city yet, but you can "marge" two cities - building them close to each other, with border in the middle.
As pre-tester and press guy I've built city with 1000 people and 300 in second, but simply border divides them. One city is sending food to the main city, and the bigger one sends stuff like boots and clothes to second one.

OFC still, these cities are TWO separate things.