David Rumsey's collection of period maps worldwide are available online to view and use. Some of the old railroad maps are there as well as general maps printed by many various mapmakers. This is a great tool for those who want to find routes and visualizing the travels of old letters and correspondence. I found references to towns in Texas (where I am) with different spellings. This is helpful for older covers when there isn't a date attached. I've found stampless covers for example where the the town ended in 'burgh" but now is spelled "burg". When they dropped the "h" is sometimes updated in the maps. They were updated frequently to adjust for the westward expansion in the USA. Thought you might enjoy.
http://www.davidrumsey.com/