I've chosen this site for a few reasons. I love Pennsylvania. I love trains. I love geography and I've got some maps courtesy of the Historic American Buildings Survey/Historic American Engineering Record/Historic American Landscapes Survey (HABS/HAER/HALS) at the Library of Congress (LOC).
To the map! This first map represents the Cambria Iron Works in 1853 when it opened. If you click on it a high resolution TIFF will begin to download.
I've been tinkering around in QGIS and have quickly georeferenced the Cambria maps series. It's a neat way to see how the works has evolved over time and space. If your new to GIS check out these links:
What is GIS? http://www.esri.com/what-is-gis
QGIS (Open Source) http://www.qgis.org/en/site/
and converted it into a KMZ that you can open in Google Earth. Looks neat with the elevation options set to 1 and 3D buildings switched on.
Clicking the above image will begin a download for a a Google Earth file of the 1853 Cambria map that you can open and explore. This one isn't so great (finding control points was a bit tough for this map) but I think you'll like the others coming over the next few days. Stay tuned!