What was once 401 North Michigan Avenue, The Hub is the centerpiece of the city; the city's tallest and most prominent building. There are 100 floors. This is where the Choosing Ceremony takes place, where children that are of the appropriate age choose what faction they will join and delegate themselves to for the rest of their lives. Peter Hayes implies that Abnegation, as the faction that control the government, have control in The Hub. It is assumed that the Hub serves as the formal seat of government in future Chicago much like a city hall. The Hub also seems to hold meetings for the city council with the representatives of each faction.
Relations to Present-Day
In real life, The Hub is the Sears Tower as it is explained in page 4. Divergent.