The name does two different jobs in the traditions that use it, and confusing them causes most of the difficulty.
In rabbinic literature Gan Eden becomes the destination of the righteous, set against Gehinnom, and the discussion is about who enters it and for how long rather than about where it was. Later Jewish mystical writing distinguishes a lower and an upper garden, the first a place of rest for the soul after death and the second a condition beyond it, so that a garden in Mesopotamia has become a stage in a map of the afterlife.
Christian usage inherits the same doubling through the Greek word paradise. It is what Jesus promises the man crucified beside him, it is where Paul says a man he knows was caught up, and the last book of the New Testament closes by putting the tree of life inside a city, so that the story ends where it began but urban rather than horticultural. Milton's long poem, which is where most English readers get their picture of the place, is a seventeenth century work of imagination built on top of three chapters.
The Quran gives an account of the garden in which Adam and his wife are placed and from which they are brought down, and it differs in emphasis: the tree is not identified as one of knowledge of good and evil, the pair are addressed together and both are said to have erred and both are forgiven. Jannah, the garden of the hereafter, is described repeatedly as gardens beneath which rivers flow.
The atlas holds the entry as a mythic world for that reason. No identification of a location has ever carried, and the tradition's own use of the name has long since moved from a map to a destination.