Add Airport

Airport could bring in supplies and people faster and would be nice fit around your city sites with monuments.

So is it not inter-islands but intra-island? It would be helipads

small airport hanger (just like the one for trains, with a runway (small) for small airplanes for more unity, give you the ability to also build cargo planes for tranding with other islands. Runway and hanger will need a lot of space... its more like an endgame thing.
with teir 2 airplanes for even more cargo throughput. Let us build the atonov An-225. Will require a very long runway=expensive to build and will need a lot of space.