Supply Building other than a city?
I've been thinking about trying to create a new building that would lay a small-ish zone of influence around it that could be used to bring resources into supply so you can build on them. Let's call it an outpost for now. The outpost would be able to station a garrison, and maybe even train units, but couldn't have improvements attached to it. It would probably provide a defensive bonus to the units inside or something as well.
Thing is:
-I don't know if this is even possible (I figure I'd need to find where cities are defined and play off of that)
-Why would anyone build this instead of a city?
That second one is what's stopping me from even starting. Right now cities just cost gold and some turns (to train the pioneer, etc). What could I do with this building (or maybe alter with cities?) that would make this building worth constructing instead of creating another city?
I figure I try to get some mod practice in before release and figure this would be good. I would have to create a tile and do all that's involved in that, then create the xml for it and get it in the game. But the first thing I need to figure out is how to make it worth building. Having it cost just materials I guess would be a start.