*'''Ancestor Tracks''' has posted [http://ancestortracks.com/ free, downloadable 19th-century landowner maps] and atlases for about 85% of all the counties of PA and will eventually post at least one landowner map or atlas for every county; they have also published books documenting the first landowners of 7 counties which are f[http://ancestortracks.com/orderonline.html or sale].
*[http://ftp2.census.gov/geo/maps/general_ref/us_base/stco2003/stco2003.pdf United States Census Bureau State and County Map]. This map will allow you to zoom in on any state or county in the United States and read the names of all of the neighboring counties.
*Historical aerial maps can be used at [http://www.pennpilot.psu.edu/ Penn Pilot]. The searches are broken into three time periods: 1937-1942, 1957-1962 and 1967-1972. There is a preview of each aerial view, but downloading maps enables the user to better magnify the area.