[Sombre]

You make a good point there. If swamp city and fortified city were the same in cost and build time, Ctis would then build in the farmland/plains provinces rather than the swamps, so they'd still be neglecting them. Perhaps in special cases like that they need a flat out awesome bonus like a fort with strong admin and defence, but also very low build time and discounted cost.

You could give Abysia really great forts for wastelands too, for instance, actively encouraging taking and holding these normally crappy provinces to get forts up on.