The plain of Lithlad is mentioned in the text of The Lord of the Rings, but it does not appear on any of the maps included in that book. It is shown on a much earlier map of Mordor reproduced in volume VII of The History of Middle-earth, and the location shown above is based on that map. From that source, we can be sure that it lay on the southern side of Ered Lithui to the east of the Barad-dûr, but its distance from the Dark Tower is open to some question. On the old map, the geography of Mordor is rather more condensed than it later became, and Lithlad is shown east of both Barad-dûr and the source of Mordor's northern river, which were at that time relatively close together. On the final maps they're much further apart, with the river now so close to Mordor's eastern borders that it seems to make little sense for Lithlad to lie beyond it. For that reason, the map above takes the name Lithlad to refer to the relatively well defined 'bay' in the mountains northeast of Gorgoroth, though this is arguably open to interpretation.