Edward Brook-Hitching, The Phantom Atlas: The Greatest Myths, Lies and Blunders on Maps (London, 2016).
Interesting information about places mentioned by Poul Anderson and Neil Gaiman:
The Phantom Atlas summarizes the story of Atlantis and Anderson, of course, wrote The Dancer From Atlantis;
Hy Brasil (scroll down) was purged from maps only as recently as 1865;
the opening and concluding chapters of Anderson's long novel, The Boat Of A Million Years, are entitled "Thule" and, in the former, the central character, Hanno, joins the northern expedition of Pytheas whose lost account is cited in The Phantom Atlas.
There are Brendan's Islands on Anderson's fictional planet Avalon and there was a fictional St Brendan's Isle on maps of the Atlantic well into the seventeenth century.
Also relevant here is an earlier post, Anti-Magic.

