Sandra, on the 1911 census web site, go to advanced search then click the ? next to the census reference field. The explanation of RD SD etc are given. Ian Sandra Trapp wrote: > Hello, > > Looking at the 1911 census, I have a question about the reference numbers that are listed, i.e., > RG14PN27195 RG78PN1554 RD502 SD1 ED19 SN12 > > > > I assume the PN in RG14PN27195 stands for piece number. If so, why are there two register general numbers along with a piece number for each of them? > > > > The ED19 is the enumeration district number, but what are the RD 502, SD1, and SN12 numbers? > > > > Thanks for any help. >