Wow! Thanks for your work.

> ; only lake fish
> reqs =
> { "type", "name", "range"
> "Terrain", "Lake (Fish)", "Adjacent"
> }

Do you plan to give city a bonus if it's adjacent to at least one Fish tile?
I think tile bonus (such as increase to food/shield/trade) applied to every applicable tile adjacent to city center is more like what you are after:

reqs =
{ "type", "name", "range"
"Resource", "Fish", "Local"
"Terrain", "Lake", "Local"
"CityTile", "Center", "Adjacent"
}

As range here for Resource and Terrain requirements is "Local" (the tile itself) it's guaranteed that it's the same tile fulfilling both requirements.

Hm, I see what you're saying, but there's no reason it should be limited to a terrain+resource combination. You could reasonably require other combinations of properties on a single tile: terrain, resources, specials, roads, bases, a city, ...

e.g., Terrain(Mountains) + Resource(Gold) + Base(Gold mine).

So rather than calling this "Resource", I think it would be a new universal called something like "Tile" or "TileProperties". Its argument would have a mini expression language for specifying combinations of things (possibly with some disambiguation syntax for the case where, say, a special and a resource have the same name).

Off-hand, I don't see any reason in principle why such a thing couldn't be done; I think the most complicated aspect would be for those parts of the system that take apart requirements and try to analyse them, such as the AI (to work out how to meet them) and the on-line help.
I think those things suggest that the expression language should only be additive ("Lake AND Fish", but not "Plains AND NOT Road"), at least at first.
Covering all tile properties with this is unlikely to be much more work than just Terrain+Resources.

However... knowing how much effort we have available, I'm inclined to aim for the simple Resource universal first, because that should be easy and obvious, and gets you some capability before we get round to the complicated thing.

Thanks. It would really expand the possibilities of what can be done. One of the reasons I wanted to do this was so that I could lower the output of some specials unless an appropriate facility is built in the city (which may have a tech requirement).