It's strange that few share their work on this subject. The few I've seen are for Star Wars, usualy backwater towns like Mos Eisley, Mos Espa, etc.
For example, this is the map of Mos Shuuta that comes with FFG's SW EotE Beginner's Game:
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This is a Map made by Ruakar depicting a section of Lothal capital city from Star Wars Rebels. :
A more complete map of the Lothal's capital city.
Another city made by Ruakar, this time from some backwater place like Tatooine:
Another one by Ruakar, but this time a more developed multiple level city:
I know a few other Star Wars forum users that make city maps, but they are only a small portion of them actually share their maps with the community and a good deal of them only do maps on paid requests, so they usualy don't share too much, just enough to wet potential customer's appetite.
It is a pity that I don't know what kind of code is used in things like Smart Building Tool in FM8 or its equivalent in City Designer for CC3+. If I could see their code, I could understand it and develop a similar code for sci-fi setting like Star Wars, Star Trek, etc.