What is the setting of Mockingjay?

The setting in Mockingjay by Suzanne
Collins on a broad scale is  Panem, a futuristic country centered across the long-ruined
remains of the United States.  Panem is comprised of twelve districts and a Capitol,
which rules over the outlying districts harshly because of a poorly staged rebellion
that happened more than seventy years ago. 

In
Mockingjay, the districts rebel against the Capitol, and the
setting of the novel shifts to follow the action as the main characters move in battle. 
The novel opens with Katniss Everdeen, once dubbed 'the girl on fire' from the Hunger
Games, sifting through the bombed-out wreckage of her home, District
12. 

The action also leads Katniss to District 13, the vast
underground city that has challenged the authority of President Snow and the Capitol.
District 13 is one of the most novel settings in Mockingjay. Built
entirely underground, the district has streamlined its citizens' lives; schedules,
activities, clothing, and diet are extremely uniform and regulated. Katniss
comments:

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"They're so frugal with things here, waste is
practically a criminal activity"
(18).

Even though Katniss
finds this environment stifling, District 13 is free from the Hunger Games and the
cruelty of President Snow, so her new home offers the hope of the kind of freedom that
all the districts could enjoy if their rebellion against the Capitol proves
successful.