I'm probably missing something here -- or missed a in game tip -- but how do you harvest strategic resource?
For example, I want the Niter in my region. I own the tile and I'm working it. I have a farm improvement on the tile.
I completed the research to Gunpowder several turns ago (which revealed the deposit).
Despite the above, I see no indication of access to the resource and I can't figure out what improvement I might need to build (if any) to get it. So, how do I harvest this strategic resource and more broadly, how does this system work in Civ6. In civ5, this all seemed automatic... It makes me wonder if there is a bug or something...