Literature and cinema, our normal means of escape from everyday life, have created places that fill our imaginations. Authors and fans alike flesh these places out with their own history and geography. The internet allows you share in the magic of creating worlds that don't exist, except in our minds. I'm sure you'll be familiar with at east some of these places, but you might not realize how well-documented they are.
L. Frank Baum wrote fourteen books about the Land of Oz, and constructed the first maps of Oz himself. These grew over time to include more detail (as more books were written) and even to include the surrounding countries.
Allakhazam's Magical Realm has a vast database of geographical knowledge of the Star Wars universe. You can look up planets and space maps, with information on the astronomy and culture of each. The entry on Tattooine features this interactive map, on which you can click for information about an area.
More maps of places that aren't, after the jump.
Maps of Atlantis have been around since ancient times. This one is from Ignatius Donelly's Atlantis: the Antediluvian World, 1882. You'll find more maps of Atlantis at Sacred Texts and at Lost Civilizations.
This interactive map of Mordor (from the Lord of the Rings Trilogy) is based on a detail of Tolkien's Middle Earth by artist John Howe. Mouseover to see place names, and click on an area to learn about it.
Star Trek Cartography has maps and charts of the Star Trek Universe, spanning the Milky Way and beyond. You can look up political boundaries, scientific data, and the journeys taken in some of the Star Trek movies.
Just last week, rfjason posted this overlay showing the size of the Starship Enterprise (NCC-1701-D) in relation to Seattle. He also has comparisons with Washington, Rome, St. Louis, and New York.
Moviefone has an interactive map of Narnia, as depicted in the movie The Lion, The Witch, and the Wardrobe. Click on an area to bring up information and scenes from the film. Click on the lion to follow a character's path through the kingdom.
Kymaerica is all about a continent that looks similar to North America, but exists in a parralel universe. You'll find insanely detailed information about the geography, history and culture of this world.
Alternate history doesn't deal with an imaginary place, but is a "what if" game that can include existing but different geography. In NEU-YORK, Melissa Gould created a map of what New York might look like if the Nazis had won World War II. Detailed closeups are available at the site.
Find more at the Dictionary of Imaginary Places.