Yeah, going "tall" in Humankind is different than Civ even.
In Humankind each city occupies/controls an entire territory. You can then build outposts in other territories to access the resources before building cities there. This is nice.
But, these outposts can then be either absorbed into an adjoining city territory, making the city territory larger, or be converted into a city itself.
The larger the territory a city occupies the more spaces/hexes it can develop for resources.
So conceivably, you could build a very large single City-State by just joining all outposts to your capitol. Or build a nation with lots of cities.
Also, units, scouts and military, use up a citizen points from the city they are built in. So you can't build too many with out depleting the abilities of your city. So large cities can grow pops faster an therefore could make more units, but they can only do one thing at a time - develop plots OR build units OR develop the city.
The demo was limited to 100 turns and/or 2 Eras, so it was hard to tell which works better or even if there is a "best" way to play. Probably somewhere in the middle, large central city with smaller outliers.
I can see a very cool balancing act developing.