How tall is reasonable?

[Abaxial]

I know if you work at it REALLY hard you can win a game with only one city, but assuming you are a casual player playing a relaxed game, what would you say was the minimum number of average-quality cities needed for a comfortable victory?

 

[Kouvb593kdnuewnd]

Building large cities are good but playing actively small is discouraged by the mechanics. How many cities you need probably depend on the quality of the land but one city is possible and more basically make stuff easier but the quality of each city is also important so just building as many cities as possible is not always the best option and generally capturing cities have much better return than building own cities.

 

[Victoria]

minimum number of average-quality cities needed for a comfortable victory?

It is very dependant on both victory and difficulty but also just how relaxed you are.
I think we still come back to the 10 city number roughly being relaxed perhaps less for CV and more for SV.
RV is the odd one out, 3-4 can be just fine.
Dip V is all over the place and more dependant on other factors than size I imagine.

 

[ezzlar]

I usually go for 8 cities. Luxury resources are distributed in numbers of 4.

 

[UWHabs]

Personally, I find that in any game, I have 3-5 cities that I truly care about, that I put effort to getting the right improvements and the right districts, and to maximize the city. The rest of my empire most of the time just does busy work, builds things here or there, but I'm not really actively managing, although I will say that sometimes those cities will become well above average cities.

Now, those other cities do provide valuable resources/districts/adjacencies/bonuses/etc... that my core needs, so I think not even having them at all would seriously hurt you. So if you didn't settle those marginal spots and only focused on a core? Hard to say what you want.

 

[Icicle]

What map size are you playing on? On standard I find that about 8 really well built up cities is fine, but that's normally because I have another dozen or so ones that aren't.