The Dome and Outside of the Dome
The Dome is where all of the "Best and the Brightest" families were escorted to before the Detonations. In the Dome, people ( called "Pures") live a very structured and almost artificial lifestyle. Male children are schooled in the academy, where they are given genetic coding to make them better at sports and school; they're all basically LeBron James and Bill Gates combined.
The very best of these children are then trained to become Special Forces soldiers. But female children aren't given as much liberty as males; they aren't allowed to have coding, and most of their schooling involves the teaching of skills needed to take care of the household.
Inside the Dome, day-to-day life is eerily similar to the lives we lead today; they have sporting events, dances, and kids form cliques and whatnot. But an aura of fear and uncertainty still lingers in the Dome. Sure, everything might seem perfect, but no one is truly unique. They're cut off from the "wretches," and trapped in a corrupt bubble of a civilization.
The outside of the Dome is inhabited by those who survived the Detonations, but were fused to their surroundings. It used to be what was called America (the main character used to live outside of Baltimore)… but no one calls it America anymore. Ash falls from the sky constantly, and people live in a brutal, dog-eat-dog world. See someone who poses a threat to you? Kill 'em.
But for the most part, survivors work together to live and resist the OSR (Operation Sacred Revolution). Still, beasts and immensely disfigured creatures make outside of the Dome an extremely deadly place. Even the place names are terrifying: the Deadlands, and the Meltlands are both places that we would never book a vacation to.