Coastal cities:

Currently, they simply don't really exist since you can set up your outpost far into the mountains and, as long as the territory has coasts, you'll be able to have a coastal city that produces naval units.

It's not game breaking, but the final result can be visually jarring, with harbours that are placed for efficiency at the far end of nowhere.

In addition, this freedom also reduces the strategic value of harbours, coastal cultures and naval units.

A few ideas on how it might evolve:

1. Harbours could have adjacency requirements similar to other districts or even more strict and have to be connected to the central plaza.
2. There could be additional sea resources (maybe just a generic "fish" tile) that could balance the coastline in the early game, before the harbours can exploit more coastal tiles. 
3. Some cultures could have traits/bonuses that apply specifically to coastal districts (for example, extra research/food/production/etc. on coastal districts)

Expanding cities in general: 

I also have a minor issue with the adjacency requirements for expanding cities. Simply put, with the current system, you sort of have to create less than efficient districts in order to reach interesting areas and/or, depending on the size of a territory, you can end up only exploiting a fraction of its interesting tiles because the rest of them are just too far away (at least until later eras).

The other drawback is that this system strongly pushes the players into creating cities that cover entire territories which, by the mid/end game look a bit unrealistic.

Of course, It's not a big issue, but it can be a little annoying for players who are not looking to recreate (Star War's) Coruscant or (Asimov's) Trantor and have an end game map that looks realistic, with cities and villages throughout the empire, rather than a city world.

A few ideas on how it might evolve:

1. maybe the makers and farmers districts shouldn't have adjacency requirements? That way we'll end up creating a town centre surrounded by theatres, research districts, wonders, etc. and the rest of the territory could have farmlands and productions areas.
2. an alternative could be that the fortress district or the artisans/mines improvements could act as regular districts and allow the connection of further districts to them. That way you'd have territories with a real city centre and small islands of development that would look like smaller villages.

Thanks for reading this.

I agree with these thoughts on costal cities and city expansion. I didn't particularly like how we could put harbors literally anywhere without and influence of city center location. I also agree that they should add "outpost" or "village" districts to add islands of development away from the city center in large territories. It seems like there's too much emphasis on city center building and any productive player would end up covering the entire map with districts eventually. I think there needs to be some bonus that you may choose that will give bonuses to undeveloped tiles in a territory, to prevent this.  

We already have villages, they are however called hamlets and only avaliable in medieval era and cost as much as harbours. I think they want city center placement to be important, by making various districts be placed freely, you reduce the importance of the city center location, so I'm not sure it is a good idea. I could see hamlets being moved to ancient era, maybe reduce their industry cost significantly or removed completely but add influence cost so you have a way to play tall with your influence. Right now there don't seems to be many ways to spend your influence.

Harbours, I think the placement rule is good, what I could see changed is that districts placed next to the harbour gets and or give major adjacency, making it very attractive to place other districts next to the harbours. Maybe also the harbour should have levels like in endless legend. Level 1 harbour would be a harbour next to no districts and would be like what it is currently. Level 2 harbour would need 2 adjacent district or a city/administrative center (to encourage costal placement. Level 2 harbour would exploit 4 tiles away in each direction and a level 3 harbour would need 4 adjacent districts or a city center + 2 other districts and would exploit 6 tiles away in each direction, but these harbours would be rare if you don't have it next to the city center.

Goodluck wrote:

We already have villages, they are however called hamlets and only avaliable in medieval era and cost as much as harbours. I think they want city center placement to be important, by making various districts be placed freely, you reduce the importance of the city center location, so I'm not sure it is a good idea. I could see hamlets being moved to ancient era, maybe reduce their industry cost significantly or removed completely but add influence cost so you have a way to play tall with your influence. Right now there don't seems to be many ways to spend your influence.

Harbours, I think the placement rule is good, what I could see changed is that districts placed next to the harbour gets and or give major adjacency, making it very attractive to place other districts next to the harbours. Maybe also the harbour should have levels like in endless legend. Level 1 harbour would be a harbour next to no districts and would be like what it is currently. Level 2 harbour would need 2 adjacent district or a city/administrative center (to encourage costal placement. Level 2 harbour would exploit 4 tiles away in each direction and a level 3 harbour would need 4 adjacent districts or a city center + 2 other districts and would exploit 6 tiles away in each direction, but these harbours would be rare if you don't have it next to the city center.

Completely agree on those thoughts.

1. Harbors should indeed give/have some adjacency bonuses o make it interesting to get quarters built near it (some interesting bonus for gold from trade routes or adjacent money quarter would be cool). At the same time I support having only one harbor per territory  and the fact that you can't randomly build quarters around it.

2. The game allows you to build coastal cities (and I've seen AI cities built on the coast), either current map or general yield adjacency system doesn't favor going for it. It's way easier to focus on mountain/forest areas to get huge production boost. 

Although to be fair I built one of my cities near the coast in the north (the territory with two leads) but that's primarily because of science tiles (geysers) located pretty much next to the coast line.

3. In general there isn't much to do on the seaside especially in the ancient/classical era - while naval units can do some exploration and help you meet other cultures and IPs there are not much benefits from having more than one pentekonter.  There aren't many resources on the sea to explore and collect, anyone to fight or coastal lines to ransack or build outposts.

There is a great cost reduction for sea trade routes (and that's amazing), however without pirates or any forms of threat for them your fleet is pretty much only for exploration.