Has anybody ever thought about building suburbs for your major cities? If you can build farms around the radius of your city, why not build a suburb in that square? They can increase the population limit of your city like the Hab Complex (SMAC) does. Maybe increase your pop. limit by one per suburb.
Suburbs could be built by colonists/settlers/engineers or purchased like terrain improvements from the city screen. Suburbs could be built on every square adjacent to the city. Accordingly, the city radius should expand.
On a related note, a major city with suburbs can function as a capital of the region or state or be the government of the region.
Thanks for listening,