I downloaded the 1940 Census data from IPUMS and included the variables: ENUMDIST and SUPDIST. In the case of Los Angeles, the enumeration district/supervisory district numbers do not match those on the microfilm (paper version) for 1940 NARA. For example, the microfilm says Sup. Dist # 1 but I only see 190, 590, 600, and 601 in the dataset. How do I make sense of the IPUMS data and the microfilm census records on NARA? Thanks!
This is a known issue in the 1940 100% file. Enumeration district identifiers are formatted as two sets of digits separated by a dash. The SUPDIST value in the 1940 100% dataset is actually the enumeration district prefix (the digits proceeding the dash), while the ENUMDIST value gives the suffix. Unfortunately, the Supervisory District data was never transcribed for the 1940 100% file, but the combination of state (using STATEFIP or STATEICP) and enumeration district (combining SUPDIST and ENUMDIST to construct the full identifier) does uniquely identify the enumeration districts. The IPUMS USA team is working to correctly identify ENUMDIST for the 1940 100% dataset, but until then you can construct the full identifier by combining SUPDIST and ENUMDIST.
I hope this helps!