Alright, speaking to my original intentions;
There are a dozen or so settlements of 150-300 people. The settlements are built into things like underground skytrain (a fancy name for an elevated monorail track currently used in Vancouver) stations, underground parking garages, sub-basements in storage complexes, uh ... what else ... underground malls, office buildings with basement levels, though the above ground portions of the structure are likely crumbling.
The settlements are like ... inventive shanty towns. Because very few settlements have access to vehicles that will run in this weather, and because having and using one makes a group a target for raiders, there isn't really the options of undertaking massive construction projects. Imagine what kind of building materials you could functionally carry through a frozen windstorm at best, and a snow-blasted hurricane at worst. Some places are obviously better designed from the get-go to provide certain functions. In the case of my example, the freezers of various sizes provide the option for offices and private quarters for important people, but everyone else sleeps in the big warehouse space, maybe with like sheets, or recovered junk from somewhere nearby.
There is no large central settlement for a few reasons; There isn't enough room indoors. In your insulated space, you need to house people, store supplies, potentially grow food, house and maintain the lighting and heating rigs you're using, plus whatever you're using to power those things. Also, the bigger you are relative to other settlements, the bigger a target you are for raiders, whether it's a direct attack, or a siege. Always knowing where people are heading gives raiders the advantage. Finally, larger settlements are harder to organize, harder to keep in line. Supplies run a little short, rationing starts, suddenly everyone thinks they can run the place better.
So to the actual environment,
@Nyx , I've made a change or two, so that the cold isn't literally extraterrestrial. I've edited everything to reflect a daytime temperature just slightly warmer than the coldest inhabited place on earth, and a night time temperature just slightly warmer than the coldest place in Antarctica. No more lung-freezing, that's supposed to be over since the vortices stopped :P