I wrote about the 1940 U.S. Census Enumeration District Finder
prepared by Steve Morse and Joel Weintraub three weeks ago.
Joel alerted my to Ginny Somarstrom's post Getting Ready for the 1940 Census
on the Seattle Genealogical Society President's Blog
written on 15 July. Ginny provided a link to the National Archives ARC website that has the 1940 census maps of the Enumeration Districts. The link for the Search is http://arcweb.archives.gov/arc/action/BasicSearchForm
It is best if you put 1940 census maps [county name] [state name] in the Search box. I put 1940 census maps san diego california in the Search box, and received 10 matches. Eight of the ten matches had the "Digital Copy Available" icon to the left of the title. I picked one of them, the one for 1940 Census Enumeration District Maps - California - San Diego County - San Diego - ED 62-1 - ED 62-142, and there are four tabs on that page. The one for "Digital Copies" brings up the maps in a thumbnail view. There are 36 maps for this particular item.
I scrolled through the thumbnails and found my grandparents area, and saw this map:
This screen image is of the map with my grandparents home block on it (bounded by Hawthorn, 30th, Ivy and Fern Streets in San Diego). I saw no easy way to zoom in or out on the web page. I saved the page as an image, and was able to use my Photo Viewer to zoom in and out.
The Enumeration District numbers appear to be written on the map - they're very faint in the images for San Diego (likely written in a colored ink that doesn't show well on the images). For my grandparents home, the ED seems to be 63.
One of the benefits of these maps, from all over the United States, is that you can see the street names, and the housing development, of the cities and towns in 1940. I'm a map freak, and love stuff like this!
Thank you, Ginny, for the lead, and thank you, Joel, for the notice on this!