Swuul wrote: ↑Wed Sep 28, 2022 6:07 am
This is a list I wrote myself during the Persia beta, not absolutely sure it is still 100% correct, but probably not many big changes at least.
Plain
Hemp, Grain, Amber, Fish, Honey, Horses, Cattle, Coral
Forest
Furs, Wild Beasts, Lumber*3, Nuts*2, Fish 
Hill and Arid Hill
Iron, Tin, Lead, Copper, Silver, Marble, Stone*2
Mountain
Iron, Gold, Wild Beasts, Silver, Copper, Sulfur, Stone*2
Alpine
Gold, Silver, Sulfur, Stone*4
Marsh
Drugs (aka Herbs), Papyrus, Salt*2, Fish*2, Naphta, Amber
Steppes
Incense*2, Horses, Hemp, Honey, Figs
Desert
Sulphur, Naphta, Dates, Figs, Myrrh, Incense
For the chance of finding resources I think only Pocus knows the formula, but I *
believe* the procedure of the regional decission to be: 
Roll 1D10. If the result is 9 or 10 nothing was found, if it is a 1 to 8, consult the rows for that terrain type. A new resource is found matching the row, unless that resource is already in that terrain, or if that column shows empty for that terrain type (and you thus find nothing new in either case).
As for where to use the regional decission, don't use it in a region where you yet don't have Stone or Lumber and where the chance to find either is higher than 1 (because you are then very likely to find Stone or Lumber, and both of those can be "found" with buildings too -> would be a decission wasted, in my opinion).
Forests are the absolute worst places to have a decent chance find anything useful. Especially if you already  Wild Beasts or Furs in a forest region, then it is in my opinion never a good idea to waste a Prospect decision there. Alpine is a close second, you are very likely to find Stone or nothing, especially if the region already has Gold, Silver or Sulphur.
If I have a Marsh without Herbs, Papyrus, Naphta or Amber, I tend to roll the dice and use the Prospect decision there. Each of those four rare resources would be a great boon.
Hills and Mountains are always worth prospecting, if they don't have any metal resources yet. Yeah, the chances are you will find nothing (because you either found stone or found nothing), but each of the metals (or Marble) would be nice to find (especially if you yet don't have any of those in the neighbourhood yet).
 
Also note that Plains actually have some pretty decent resources. If you have a plain region with just one or two resources, it might very well be worth to Prospect there -> nothing super exiting to be found, but all that can be found provide economic boost through synergy with buildings (in this region or adjacent ones).
Steppes and Deserts have some nice resources to be had, but they also have lots of empty columns. If you feel lucky, you might want to Prospect a region with only one resource, but don't have too high hopes of actually finding anything.