I just discovered an interesting site for Twain enthusiasts.  The library of
Congress has a map collection at:

http://memory.loc.gov/ammem/gmdhtml/gmdhome.html

Search for Hannibal in the "Panoramic Map" collection.  There is a panoramic
hand-drawn aero view map of Hannibal (1869).  It's fun to zoom in on various
places familiar to us through Twain drawn not too long after he left his
boyhood home.  My only question is how the artist got up in the "aero" to
sketch the town.

Have fun,

John