CaiusDrewart
King
The problem with settling on the coast is that sea tiles AND sea resources are useless. They've lowered the yield form Civ5, while all other yields in the game have gone up - sometimes hugely.
In addition to the existing bonuses, the district buildings should:
Harbour: +2 gold if adjacent to city centre. Encourages cities built on the coast, and makes cities built near the mouth of a river a beast when you take into account the commercial district adjacency bonus.
Lighthouse: +1 food on each sea tile. Speaks for itself.
Sea port: +1 gold on each sea resource
Shipyard: +1 hammer on each sea resource
This brings a fully developed sea resource in line with a good land tile, which is what it should be. Plain coastal tiles are now about as good as unimproved land tiles. Again, as it should be.
But coastal city centres need something more than a beefed up harbour, they need their own special buildings (like river cities get the water mill). I would add:
Wharf (available with sailing): city centre must be adjacent to coast. Gives +1 food, +1 hammer.
I doubt it would be particularly helpful but I think it would be fun to add
Coastal fortress (available with balistics): city centre must be adjacent to coast. Gains an additional ranged attack, can be used on sea tiles only.
This would tempt me to build cities on the coast, maybe even at the expense of fresh water (provided an aqueduct is still in range). But not anywhere near enough to make them OP.
I think these suggestions are really good. I love the coastal fortress flavor-wise.
It's really sad how useless coastal cities (and therefore navies) are on a normal map.