A Futuristic, Dystopian Chicago

The city where Tris lives isn't the Chicago we know. For one thing, there's a giant fence that locks everyone into the city  for another thing Lake Michigan has become a swamp and for yet another other thing, large parts of the city are crumbling or in ruins. It's now "a patchwork of new, clean buildings and old, crumbling ones" We never learn what happened to Chicago, but we can be pretty sure that it wasn't so good. Through the story their is proof that Tris is in Chicago, When the Dauntless go to play Capture the Flag paintball, Tris climbs the "Ferris wheel at Navy Pier".

Demeanor

the way a person behaves toward other people

The gray clothes, the plain hairstyle, and the unassuming demeanor of my faction are supposed to make it easier for me to forget myself, and easier for everyone else to forget me too.

    Supersede 

take the place or move into the position of

Faction customs dictate even idle behavior and supersede individual preference.