Unique Locations

So, I’m back to working on my terrible mods. But still, one issue remains: I cannot figure out how to (if it’s even possible), create a unique location, as in a location that may be generated only once per map. Ideally, I’d like the location only to spawn if you chose the appropriate spawn location, but even just the ability to have a single of this one map tile type would be great. Thanks in advance for your reading/replying.