Derek will have more on this soon.
But after much back and forth, it was decided that we're not going to have 1 tile cities. Instead, they'll be just a few tiles (much much smaller than what we have currently). The objective being to let players see at a glance what the city does.
Improvement categories will upgrade into better versions.
For example, right now, you would have a study and a school and a library and a college and a university and on and on.
Not only does this use a lot of physical space in the world, it also makes it hard to tell what that city is specializing in (not to mention that the old city system doesn't lend itself to specialization so you just end up having a bunch of generic cities).
A typical late game city might be using 24 tiles. Now, it'll be more like 4 to 5.
Having the smaller cities has also let us decrease the # of tiles between cities from 8 to 6.