It would be interesting to cross-reference the records from Freddie and Fannie with the HMDA data, which has additional fields about each mortgage application: https://www.ffiec.gov/hmda/hmdaflat.htm Would the HMDA "loan amount" field match the "ORIGINAL UNPAID PRINCIPAL BALANCE" field in the Fannie data? Since HMDA data is geo-located to the Census tract, it could then be linked to Census and other public data sets.