As in general, all grassland and plains tiles (flat and hills equally) are post-bio running state property FP=5, and the city tile itself has F2P1 for FP=3, any city that has only grassland and plains tiles and no resources at all can reach FP=103, although you need F=40 so you end up with P=63. Getting F=40 depends simply on being able to chain irrigate into the fat cross for irrigated post-bio farms (except for 20 flat grass tiles where 20 workshops do the job).
So, almost any city can be made a production city late in the game.
However, we need production way earlier than that. Having simply 20 grassland tiles doesn't make a production city early on. It'll make superb cottage cheese though, which is why you almost never see those 20 workshop cities in the endgame either - scrapping 20 full grown towns for workshops is just too painful to think about
When I think about cities early in the game, I first consider their food potential "now" and "post Civili Service (chain irrigation). See what's the maximum food surplus for the city with only the resources improved. That's the amount of food I can use for whatever the city is going to be.. If the food surplus is very large, I consider GP farm. If the food surplus is high and the city has lots of hills, I consider early production (plains hills are great for hammers but you need that food surplus for them). If it has minor food surplus and lots of cottable tiles (flatlands and grassland hills), I start counting how many cots I can run there, how many farms do I need extra, and if it might become a good commerce city.
Oh yes, I mostly run CE, as SE requires more micromanagement. I hate that
One reason I have hard time moving to Monarch, I can be lazy and weedy and still get off the hook on Prince, but on Monarch I just can't do that, have to actually concentrate on the game
So, a city that has some hills and some food surplus. If I can get the city to maybe size 8-10 pre-CS with 15+ base hammers, it's probably production city. Then I consider the long term: can it grow to 12-14 pre-bio pre-sp while consistently getting more hammers out of every citizen? If not, have to think about it still - maybe it's not good midgame production city, only early game and late game one? But if yes, then it'll make a midgame production city as well, and as noted, anything can be made production in the late game.
And as said, resources definitelly affect this. A city with pigs, corn, and copper, with half a dozen hills? Definitelly production.
