What is the setting of Catching Fire by Suzanne Collins?

The novel is set in the fictional, post-apocalyptic world of Panem. The reader suspects that Panem is Earth after some catastrophic event that left it struggling to survive and therefore grown into the oppressive government it now features. Panem is divided into twelve districts that each has its own industry. Many of these districts feature a Justice Building that appears to be a remnant of Earth before the unknown destruction.