I'm not sure how this was done, or how cell towers really work (or where they exist) but many of them appear to be in lakes, rivers and so on. What's wrong here, my understanding or the map?
Most of them are duplicate entries but with different levels of accuracy. So the same tower may have 10+ cell sites on it. So its represented 10 times. Multiple carriers in multiple technologies. Whenever they were mapped, possibly over years, the granularity level of GPS coordinates were different, so a lot of them are just in the general area.
it's based on where the single was picked up the final coordinates are calculated. Signal travels much further in open water therefore you can pickup very distant cells, skewing results.