The crop resources (and to a lesser degree, bullion, lesser because I've had more landowners than traders) were one of the more confusing things to me as a new player. Mainly, the question of, "what counts as a crop?" I see now that if I middle click on a tile with Wheat, and hover over the "Wheat" resource, it says it "Unlocks Crop Resource". But it took me a game or so to really grok that I can middle click anything for tooltips. That first game, I would open the Old World-Pedia, search "crop", not find it, and then search "Landowner" to find the answer.
Why was it confusing? In part, because while all farms count as crops, only one grove counts as a crop. Wine doesn't count, although grapes are crops, and the same applies for olives. I reckon this is probably for game balance reasons, but that was why I was checking a lot. Should I give this new city to the landowners or the other family? It has a lot of wine and lavender, are those crops? Now I know they aren't, but it wasn't obvious at first.
A couple ideas for making it easier would be adding Crop and Bullion entries to the Encyclopedia, and having the Settler option to found a city for landowners/traders tell you how many of the applicable resources would be in the initial city area.