The Internet is a great resource for research. Maps, particularly older maps, have only more recently been made more available to the general public online. Some of these sites charge for various services, such as prints, though most are free to at least view the maps. The following sites are recommended websites for obtaining old maps (road, topographical, or otherwise).
David Rumsey Collection – This site has numerous types of maps including oil company road maps, maps from state governments, and much more. Old Caltrans (Division of Highways) official state maps as well as some California Highways and Public Works can be found on the site as well.
USGS Historical Topographical Maps Online – All of the USGS topographical maps produced, both new and old, can be found on this site. I highly recommend a visit to this site. As a result of this site, I have since donated the bulk of my map collection to the Los Angeles Public Library, retaining a few important maps for myself in the process.
Historic Aerials – This site has old maps and old aerial photography available using overlays as well as other methods to compare new and old images. I have used this site extensively to help determine route locations, alignments, and older land uses in my research.
With any of these sites, keep in mind that older data may not directly overlay properly to current data. This error can result in confusing data, such as erroneous highway alignments and conflicting map data. Even with official maps from governments, there is always a chance for errors. Some maps from the California Division of Highways have either incorrect or misleading data showing State roadways in either the wrong location or mislabeled. Even with this caveat, these maps are invaluable research tools and are very helpful for what they are – windows to the past. If you have a mapping site that you have found to be quite helpful, please let us know and it may be added to this list.