These books are available at VCU Libraries in paper and/or electronic format. Find them with the VCU Libraries search page.
Here Be Dragons: Exploring Fantasy Maps and Settings by Stefan Ekman
Middletown, CT. 06459: Wesleyan University Press, 2013
Literary Wonderlands : a Journey through the Greatest Fictional Worlds Ever Created, edited by Laura Miller
New York : Black Dog & Leventhal Publishers, 2016
The Routledge Companion to Imaginary Worlds, edited by Mark J. P. Wolf
New York : Routledge, 2018
The Writer's Map : an Atlas of Imaginary Lands, edited by Huw Lewis-Jones
Chicago : University of Chicago Press, 2018
For more, search for the subject Imaginary places in the search page above.
It seems that the biggest collections are now just found on Pinterest! But below are things that I and others have found.
And if somebody has additional suggestions for a great web-based resource, I'll be happy to list it here: just let me know (Eric Johnson, firstname.lastname@example.org).