Fearing a west coast invasion during World War II, the U.S. Department of War collected airphotographs of all of Sonoma County in 1942. These photos are the earliest complete image of Sonoma County. The photos were collected on film and printed as thousands of hard copy (9" x 9") photos. Two complete hard copies remain - one at the University of California Berkeley and the other at Draftech in Santa Rosa.
Through grants from the Sonoma County Water Agency and the Sonoma County Agricultural Preservation and Open Space District, the San Francisco Estuary Institute (SFEI) has digitized, georeferenced, and mosaiced a subset of these 9x9 hard copy photos. The original batch, completed in 2014, covered the Santa Rosa Plain. In 2016, the Dry Creek Valley was added to the historic mosaic of photographs. At the tail end of 2017, SFEI made the latest batch available, extending the historic air photo mosaic down to the Marin County line. This dataset is useful for all manner of historical analysis such as understanding changes in land use and population, and tracking changes in vegetation and habitat over time.
The data is available as a tile service (search ArcGIS.com for 'Sonoma County 1942'), as a tif file for download and use in GIS software, and in a historic photo viewer titled 'Central Sonoma County - Then and Now.'