Im doing a total war-style empire builder in a near-future, slightly post-apocalyptic world. The player control cities and armies on a map and fight for control of the cities. Cities produces resources and train armies.

I want maps to be large scale, like the entirety of Europe or even the entire world as the playing field.

The problem is to be realistic cities would be EVERYWHERE. But thats not fun with the gameplay. On a Europe map i would like around 30 cities, so there is some space between them to maneuver. Managing 7-15 cities for a player midgame would make sense.

Now:

That means areas such as great britain, scandinavia or france would have only 3-5 cities each. Would you think that's disturbing immersion to much? What could help limit the disturbance?

I would prefer to use large-scale real world locations since it's more fun! (having huge maps makes cities and nations more diverse for one thing)

I think your setting deals with the issue directly. Nuclear war ravaged the world, destroying many cities. And then when massive warfare started up, folks either scattered into the countryside or immigrated into one of the 30 major cities capable of defending them.

Yeah Im thinking to go more into the "fantasy" setting which would allow more freedom in this question.

Most megacities would be very targeted by missiles/attacks so those areas could be completely non-visitable. And of the few cities I use as functioning settlements in the game some could even be new towns that I just make up such as "Freetown" or "New Paris" (those places got into the limelight after the old important cities was razed).

I should maybe even mark ruins on the map (as landmarks of cities such as London). No gameplay effect, just for flavour.

This is directly linked to the scale your battles plays at. If you are showing a large scale map of the whole of europe, adding every city in europe would make the map EXTREMLY cluttered. And if you zoom in enough for the map not to feel cluttered anymore, your player has to do A LOT of scrolling in X and Y axis to move from spain to scandinavia and so on.

Then there is the question: why do you want more than 30 cities? Because you think its realistic? First, what polama said. Add a nuclear crater at the place where major city is today, and you can flat out omit it (it will actually add a lot of flair to your whole setting while costing you almost nil in development cost. Imagine players from Berlin looking for their city on the map an finding only an impact crater and ruins where Berlin should be).

Secondly, if it doesn't add to the fun or the story, you should really cut a feature even if it is realistic. Unless its a simulator... but then picking realism over fun most probably is why simulators have gone almost extinct nowadays as a genre for home entertainment.

Your 30 cities sound totally feasible. If you game design doesn't need more cities to work, leave it at that. Fill the void between them with other interesting stuff. Ruins of the other cities, radiated wasteland, a hidden oasis amidst the desert, crashed planes, whatever. Maybe you can make these even into more than just graphical candys, maybe they give your player a strategic advantage if held (finding technological artefacts in old military bases, resources in ruined cities, food in hidden oasis, being able to reactivate some of the stuck vehicles in the desert and gain these as troops)?f

Sounds more interesting to me than overloading your map with an endless sea of cities.

Sounds good.

Having ruins be sort of like in "Masters of Magic" or civilization:

When an army of a major power first visits a ruin: spawn a small low-tier neutral army (these are locals defending their ruintown). Then offer a reward for "clearing the ruin". Could actually work fine in my game.

there's really no problem with only having the largest cities. anything smaller is beneath the "modeling level" of the wargame. as in squad level, battalion level, division level, etc for the smallest unit represented. but in this case populations of 10mil, 20mil, 50mil, etc for the smallest settlement represented. if you want to put craters where smaller cities are, that's an option, or you can just leave them off the map as being too small to model in the game. a strategy map shouldn't have every city on it, that would be a tactical map.

+1 on this.

Lesser cities and villages could be represented as merely decoration on the map.

If you think about it, in any Total War, one city per region doesn't really mean there are no people living anywhere else in the region. It is just the center/capital of the region.

One main road going through doesn't mean this is really the only road in the region. Its just the most strategically important one.