There may be 2 sources that can help you. Many states and some
counties and cities have mapping data layers available to the general
public, free of charge. Do some searches for GIS data. Start out
local and then work up to state level. 2 Missouri sites that you can
use for comparison to other states are
http://msdis.missouri.edu and
http://cares.missour.edu. some local communities have there own data
portals. San Diego has their hppt://
www.sangis.org.
Frank Wideman