Trove of Maps at DPL
It talks about historic Sanborn Fire Insurance maps that show historical views of Denver and other places. "As buildings changed, the maps were updated with paste-overs.... It's like showing geologic layers of Denver."
If you can make it down to the Central Library to look at the original maps, you should; but they're also available online for Denver Public Library card holders: Sanborn Maps Online (Library card required). The online version doesn't have the overlays, but there are maps of different dates to show the changes.
Check out an online view of the ribbon map and views from earlier Maps Exhibits.
The map collection is the focus of this year's Booklovers' Ball, the Library's fundraiser on October 9. The 2010 theme: "Explore." Tickets are on sale now!