The requiredimprovement has one big flaw, unfortunately. The buildings required have to be "inside the city walls", it is not enough that the improvement is connected to the city like a world resource OUTSIDE the city walls is.

Hopefully that will change, as it makes the temple of essence (and similarly modded buildings based on world resources) difficult to use.

I was trying to make good use of those tags, but was more interested in having my buildings be dependent on the local resources than on what I had already decided to build.

I had put a local Specialization resource in the city hub, and then created a few different level one buildings that would greatly shape the effect of the city, and each had the specialization resource as part of the construction cost. Then I had a variety of buildings that could only be built where there was say, the Capital, a Manufactory, or a Shrine.

But I found I prefer to develop improvements that are more dependent on local resources (or to make an improvement create a certain number of local resources (ie. a Seat of Power might create 3 local Edict resources that could be spent in that city only to enact a choice certain laws or policies, or a Merchant Guild could produce several commerce resources that allow for a selection of upgrades requiring a local commerce resource.

I've found it pretty powerful to create local versions of many of the resources. ie. An Iron Mine creates global metal, but it also creates 1 Iron, which is only a local resource. Mana Shards create global Shard Power and mana, but also create a local leyline. So I have a Manufactory that requires local Iron, and it's okay if that Iron is outside of the city walls. I created an Elementium Refinery which requires (and consumes) local a Iron and a local Earth Leyline. And Golem Manufactories which consume local life or death shards, as well as Clay, Metal or Crystal. It's neat to have the possibilities depend on what's nearby.

I also created a Lord's Manor to allow for exploitation of resource poor cities. It removes a Grain and Material from the local city, creates a single Global resources for Peasants and Laborers, which can be consumed in other cities to add the Grain and Material there as import buildings. I use the above tags to make the Lord's Manor a prerequisite for other buildings which unlock certain estates for Noble or Terrible Lords who are like champions, except they don't receive level abilities, and have administrative bonuses (or penalties) when stationed in cities.

I'd like to add a single Religion resource to the Capital City hub, and then develop a variety of religion based buildings around the six different shards so that each faction could found a very different (and exclusive) religion and develop the various abilities and improvements around it.