You can still build cities, but they can be located anywhere. Sorry, I wasn't clear on that. Food transportation will be a factor, but we still need to figure out a system for that. Again: "People in the city (need food and) can produce (...) commerce, science and culture" and such. And this way you will also be able to claim small islands in an ocean without having to build a whole useless city. And they will also be more stationary. If you evacuate half your population, you'll basically have unhoused refugees in your own country.
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