This is mostly an excerpt from a post about a system for handling population growht a bit more interestingly that I derived from an idea of the EB team. They gave me their ok to put it into the mod, but I nevertheless decided to present the system to them beforehand. I didn't go into too great detail about it, but the basic layout is mostly there and implemented. Since my computer broke a while ago, I can't finish it right now, but this will probably the first thing I do when I'm back on track (unfortunately, this will also be after my exams so probably not before the middle or end of February):

Ok, first of all I decided that I wanted a bit control about how large a settlement can grow at all because I don't like totally unhistorical huge cities in areas that wouldn't actually be able to support them. Therefore I implemented a growth_level tree, ranging from 0 (tiny) to 5 (moloch).

It is important to know that in II, I'm implementing the city/castle split as a urban or rural focus for a province. Urban provinces will be focused on the city while rural ones will focus on the countryside.
For the food system, this means that urban settlements will capitalize on your import idea while rural provinces will get more food production and export capabilities. Consider the tech tree below:




First a legend: Blue text means rural, green means urban (black is both); the small roman numbers are the required growth level for the building; a stroke-through line means an upgrade in the same building, a dashed line means an "and" requirement while a dotted line means an "or" requirement.

The general system works (for those who are familiar with it) like my authority feature: The player will have a "national food pool" which is increased by export buildings and decreased by import buildings. If the food pool is negative, I will trigger a starvation event for the whole nation until the player destroys some import buildings or creates more export buildings. A second option which I didn't yet experiment on is the chance to establish trade deals to import food from other factions (e.g. in II the Venetians would probably rely pretty heavily on import from Canossa or the Ottonians), I'm not yet sure how to handle it but I'll probably trigger some event on good faction relations.

Ere I forget it, the player will be able to see his food pool on his accountant (for more info read the II previews).