I've seen suggestions that 1 tile islands might be good for producing Naval Units. I've also seen speculation that Naval Units can only be built in a Naval District. Operating under that assumption, then a 1 tile island without any other land tiles within its 3 tile radius wouldn't be able to build Naval Units because it would be allowed to make/build a Naval District. Unless I'm missing something . . . are Naval Districts built on a coastal land tile or a coast water tile?