Looking for maps?
Thursday, February 21, 2008
Topographic maps are an essential tool for tracking down lost or abandoned
bridges. The quadrangles produced over the years by the U.S. Geological Survey
often show the traces of old roads and railroads. In the past, these maps were hard to find online, but the
situation has improved:
- The Internet Archive (archive.org) has posted national coverage for modern-day quadrangles in TIFF format. These maps include the "collars" from the printed editions, which include useful information such the date of revision and the names of adjacent quads.
- The University of Texas Perry-Castaņeda Library site features modern and historic 250K-scale quadrangles in convenient JPEG format. These do not include nearly as much detail as the ones above, but many areas were covered in the 1940s and 1950s and show roads and bridges from the pre-Interstate days. Also, railroad overpasses are clearly marked, something that even more detailed maps don't always show.
- The University of Alabama site features many historic quadrangles from the late 1800s and early 1900s. Select a state and then look for the "Out-of-Print Quadrangles" link at the top. Unfortunately, the site requires the MrSID browser plugin which make serious research difficult. In addition to the quads, UA also has historic soil survey maps for many counties, another excellent source of bridge information.
- Other sites with historic topo maps are listed here. Coverage is sporadic, but some parts of the country have excellent coverage with maps available in convenient downloadable formats.