Why are there sometimes more than one 1920 or 1940 ED given for a 1930 ED, and vice versa?
The district boundaries were not the same in the different census periods. In some cases several 1920 or 1940 EDs might be contained in a single 1930 ED, while in other cases a 1920 or 1940 ED might be split over two or more 1930 EDs. If you get more than one 1920 or 1940 ED, you might want to narrow things down further before you start looking through all the EDs. You can do this by looking at a description of the various EDs along with a map of the area. ED descriptions for various years can be found on NARA microfilm series T1224 (see question 5). You can obtain the 1920 descriptions online by going to http://www.ancestry.com/search/io/choosest.asp?c=3 and then select the desired state, county, and city in sequence. You will eventually get to a description of the EDs within that city. This is a free service on ancestry.com so you do not have to be a subscriber to use it. Such online descriptions for 1940 do not yet exist; when they do we will post the link. As for a map of the area,
