If you mean the railroad spam, then it's a well-known problem, and completely outside the scope of this mod.

I haven't touched the AI logic for the buildings in any way. Same goes for laws, decrees, or technologies.

Are you perhaps using the wrong mod version? As the name implies, this one is meant for the 1.6.* version of the game. It is also compatible with 1.5.*, but the newest game version needs the 1.7 version of my mod.

Please prevent AI spamming every building in every state! That's the biggest problem with MAPI. Everything is randomly everywhere. Please limit different urban building slots to 5 or something

I've thought about something like that, but sadly, the game mechanics don't work this way. You can have either a flat MAPI bonus, or a staffing-dependent bonus, but not a bonus tied to the number of buildings.

My initial idea was to have a MAPI corridor of sorts, defined by technologies and laws, then have the buildings fill it out. Sadly, it is impossible to implement that in a way that the game supports natively. On the other hand, adding some kind of script-driven, dynamic modifier would likely slow down the game to halt. It's already laggy enough as it is, without some jury-rigged superstructure.

I had hoped that they would improve the MAPI mechanic, but instead, they took away manual construction.

Cool mod! I really agree with your approach - the integration of markets wasn't really constrained by a specific innovation, but rather the capacity/bandwidth of transportation into/out of a state. Really, ideally I think MAPI would be impacted by gross goods produced/consumed in a state, because more things flowing into/out of a region was constrained by the actual availability of transportation infrastructure.

I might tweak your mod a bit to make things even more dependent on ports/railroads, is it possible to increase MAPI per level of port in addition to just from having a port in a state?