Atlanta was an American city, located in the state of Georgia. (TV: Dead of Night)
The Centers of Disease Control (CDC) was based here. (PROSE: Spore) In an alternate timeline, Atlanta was the location of the Commonwealth Disease Center, which cured many diseases by carrying out tests on unwilling prisoners. (PROSE: Republica)
Behind the scenes
Location information
Though it's possible that a real world location doesn't exist in the same geographic space in the Doctor Who universe, such cases are few and far between. Thus, the map to the right is probably a good indicator of the DWU location of Atlanta.