I got an email yesterday from the developer of a new website that's dedicated to ebook maps. There are around 200 maps on Ebookmaps.com now and they cover cities all over the globe. The maps are drawn from the Open Streetmap Project, and they''re released under a CC license.
The ebooks are available in Mobi and Epub. Each map section measures about 400x600 and they work fairly well on my K2.
It's a pretty neat site, and it's also a great idea - in concept. Unfortunately, there's a bug which adds an extra blank page after each map section.
Luckily this can be fixed easily. Someone will have to go back to the source and add the navigation buttons and then recompile the ebooks. It shouldn't take too long.