I must say I'm really tired of the Natural Park mechanism. Here's a case from my current game which is really frustrating. I would like to place a Natural Park in the area mark in this image, but I can't. Why? Because the mountain tile was originally claimed by Dumbarton, and there is no way I can ever get it to switch ownership because it is outside the third tile ring of Ayr. This mechanism is immensely stupid. They really need to change it so that instead of all tiles having to be owned by the same city, instead the ownership of all tiles will just shift to nearest city when natural park is placed.