So a warrior has a vision of 2 tiles but a settler has a vision of 3 tiles (along with a Spy, Naturalist, Varu Conquistador Observation balloon, helicopter, Rocket Artillery, Uboat, Ironclad and missile Cruiser). I know my settler and any other unit can normally see higher objects an additional tile away. In this picture below the mountain on the left is in fact visible by the warrior, If I move the warrior visibility of it goes. Also the warrior cannot see the tiles in front of the mountain because it is not on a hill and so is being blocked. However the two tiles in front of the mountain are hills and I would expect my settler to be able to see the upper one of the two if visibility is tile centre to tile centre. When my settler founds the city it loses its extra visibility as a city can only see two tiles, however it is now raised by a level and so the white square tiles are marked that it can now see and tiles 3 away it can no longer see. Here is a screenshot just showing all terrain so you can see the tiles in front of the mountain. I would have thought the settler could see the one marked as a centre to centre line does not cross another tile they cannot see over. Additionally, why can an ironclad see 3 tiles but a battleship or destroyer only see 2?