I want to roll up the IPUMS CPS data at a zipcode level. There will be many zip codes for one METAREA and that’s okay.
If I understand your question correctly, you would like to identify the zip codes contained within each METAREA. The Census Bureau provides a mapping of ZIP Code Tabulation Area (ZCTA) onto metro areas. A similar mapping for postal zip codes does not exist, because zip codes frequently change and there is no correlation between zip codes and census block boundaries. The Census Bureau creates ZCTAs by aggregating Census blocks that use the same zip code and assigning the most commonly used zip code to areas with multiple zip codes. It is possible that some very small zip codes are lost in this process, but most are represented in the ZCTAs.
See here for more information on ZCTAs. See here for the CBSA delineation files necessary for interpreting the ZCTA mapping file. Alternatively, you can create a mapping of ZCTA to metro area at the Missouri Census Data Center that might be in an easier-to-use format: select “Metro Area” as the source variable and “5-digit ZIP” as the target variable to create a mapping.
Keep in mind that the CPS METAREA variable uses the coding system from the 1990 Census. The files above use updated metro area coding; thus, the ZCTAs associated with any given metro area may not be exact. Unfortunately, the documentation does not exist for mapping ZCTAs onto the 1990 metro area codes. The Census has consistently defined metro areas as a large population center and adjacent communities that have a high degree of economic and social interaction, but it is up to the researcher’s discretion whether this potential loss of accuracy is acceptable.
Hope this helps. Please let me know if I have misunderstood your question.