I think we have separately come to many of the same conclusions regarding the problem. That either means we are on the right track or we're both about to get hit by the same train . . .
Let's summarize the problems:
- production is king and oceans can't realistically provide much production
- Water tiles can't provide too much gold to prevent 1-tile islands from becoming overpowered
- districts need space on land to be placed and coastal cities have significantly less tiles to chose from
- Even cities 2 tile inland can build ships with a harbor, 1 coastal tile within the 3 rings is enough
- Coastal cities need a separate navy for defense, while inland empires can focus on their army alone
- Coastal cities are more affected by climate change (and to a lesser extent natural disasters
Victoria will tell you that Chopping Is King other than 'Production' per se, but it comes to the same thing: Chop your sea resources and you have an almost completely unproductive tile for the rest of the game: rarely a good trade-off.
The Climate effects seem to boil down to Hurricanes and the fact that they are mobile and can affect virtually any coastal tiles, as opposed to Volcanoes and Floods, which only affect certain, easily identifiable tiles, and the other 'natural disasters' which simply aren't as devastating (at least in my experience) as Hurricanes. IF Hurricanes are brought more in line with the other Disasters in destructiveness and alleviation techniques, this problem can be solved without any other Game/Play changes.
For instance, Buildings or Districts on a hill, with a hill between them and the Coast, or even with a Marsh or Forest between them and the coast (which would greatly alleviate Storm Surge effects) could all be 'immune' from complete destruction. Pillaging from disasters is annoying, but, as I've posted before, having to keep a 1-Charge Builder around to repair disaster-struck tiles is not a game breaker: having to build new Buildings from scratch, interrupting all other construction in the city, is.
1) I mentioned the "production from population" mod earlier - it fixes a lot of issues: Food becomes more important, tall play gets a buff, coastal cities become more competitive,...
See the mod for more details and also check the additionally recommended mods like "rebalanced mines":
https://steamcommunity.com/sharedfiles/filedetails/?id=1651788601&searchtext=
Apart from this rather significant change, gold could be a realistic substitute for production to a certain extent.
I will have to try those mods, once the new Patch installs and we find out what Mods still work with it.
My own tentative Solution to Making Population Important is to bring Specialists back with a Vengeance: to get any real results out of a building would require a Specialist, and every building, including Walls and the Palace, would have one or more Specialist slots. To balance this, each population point would represent both a (in the beginning, majority) portion of the population working the land/tiles around the city, and a (initially much smaller) portion working in the city as a Specialist.
The Harbor and its buildings would have an advantage over other Buildings (but not necessarily all of them) in that their 'specialists' could be one of several types, providing Food, Gold, or Production 'bonuses' depending on whether they are affecting fishing, raw materials import and fabrication, or general Trade.
The problem is the ease of acquiring gold from non-coast-related sources, especially trades with the AI.
Solutions to consider:
- Allowing more trade routes from harbors than from commercial hubs (example: 1 TR for each harbor, but only 1 TR for every 2 commercial hubs)
- Alternatively, the number of trade routes could be: (number of harbors + number of commercial hubs + number of coastal city centers) divided by 2
- Increased yields for TR's starting from a coastal city would also be an alternative
- We could also give very strong yields to harbor buildings that double if the city center is adjacent
First and Second Points: another possibility would be more Trade Routes from the Harbor buildings. It takes no stretch of Logic to assume that a Lighthouse and Seaport would generate more trade: that could give your developed Harbor up to 3 Trade Routes without further ado.
Third Point: We agree completely on this: Sea trade routes were an Order of Magnitude more efficient at transporting goods than any other method before the Railroad, and the game doesn't begin to show this yet.
Fourth Point: Harbor Adjacencies could, I think, legitimately be from Industrial Zones, Commercial Hubs or City Centers:
Industrial Zone - Production Bonus and easier/cheaper production of ship units
Commercial Hub - Gold Bonus, possibly even an extra Trade Route or Great Merchant Point
City Center - Gold And Production Bonus, since the Palace was, at least until the late Renaissance Era, the major Market for luxury goods (from overseas) and a major center for the production of 'luxury' goods for the High Society gathered around the throne.
2) Naval trade has to be represented through bonuses to the harbor, the city center or for trade routes. Water tile yields are trivial now, because loads of gold on every water tile would unrealistically favor one-tile islands (why should the Azores have a stronger harbor than Houston, Rotterdam or Shanghai?). To avoid this dilemma, we might as well remove tile yields from water completely except for fish/crabs/whales/pearls. Those resources would mostly give food (loads of it!) and some production - but all the naval gold should come from the district, the city center and trade routes!
This might be radical, but if we are honest, the current yields from resourceless water is a trap - you're better of not working those tiles 99% of the time!
3) I believe this can best be solved through stronger adjacency bonuses between the harbor and other districts (industrial zone and commercial hub especially).
Campuses, theater squares, and holy sites could also get coastal adjacency bonuses (representing the inspiring nature of the sea, seafaring, trade and travel).
4) This problem is probably best solved by following the advice from point 3 and giving strong incentives to concentrate city centers and districts along the coast.
See point about 'extra' adjacencies to City Center versus Commercial Hub or Industrial Zone, which would incentivize putting the City Center on the coast instead of 1 - 2 tiles inland.
Addition to 3) above: Monasteries, Chateaus and similar 'bonus' structures should also get 'extra' bonuses from being on the coast. Possibly link it to the Appeal of the tile, so that the classic coastal hill/headland becomes a favorite spot for Lord HaHa's country residence or the Holy Brothers of the Webbed Foot to place their structures. - There's a golf course not 8 km from where I sit that gets extra traffic because it is located right on the shores of Puget Sound: the coast, as long as it's not raging, tends to attract people.