The asphodel meadow appears twice in the Odyssey, once when Odysseus sees the dead and once at the very end when Hermes leads the suitors down. Both times it is a phrase rather than a description: the dead are in a meadow of asphodel. Everything else about it, that it is grey, that it is for the ordinary dead, that it sits between Elysium and Tartarus, has been supplied by later readers.
Even the tone is uncertain. Asphodel is a real plant, a pale flowering perennial that grows readily on poor ground and was planted on graves and associated with the dead in Greek practice. Whether Homer meant it as bleak, as neutral, or as something closer to a flowering field is a genuine question in the scholarship, and the standard dreary reading owes as much to the general gloom of the passage as to the word.
It is included in the atlas as a useful control. Most named afterlives are built up over centuries by many hands. This one shows the process in miniature: an ambiguous phrase in an epic, a plant with funerary associations, a later demand for a middle option between reward and punishment, and a place that now appears in reference works with a settled character it was never given.
The meadow is also where Achilles is standing when he says he would rather be a living labourer than a king among the dead. The most famous statement about the Greek afterlife is made from this ground, which is part of why so bleak a reading of it has stuck.