Memphis was an American city.
Behind the scenes Edit
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 at right is probably a good indicator of the DWU location of Memphis, Tennessee.
Nevertheless, Dalek does not in any way suggest that Memphis might be in Tennessee, which this map clearly shows. Still, as a point of distinction from Memphis, Egypt, we add "Tennessee" as the most obvious way to help us distinguish between the two.