Four common variables: Family_name in the Catasto [SURNAM1 in the Online Tratte], Name [NAME1 in the Tratte], Patronymic [NAME2 in the Tratte], and Location [QUAR in the Tratte] permit you to search for individuals between the two data sets. In addition the variable Trade in the Catasto [OCSTAT in the Tratte] appears in both sets. However you must be aware of some considerations.
1) Family_name, Name, and Patronymic have 10 letters in the Catasto; SURNAM1, NAME1, and NAME2 have 11 letters in the Tratte. You need to truncate one more letter for truncated names in the Tratte when looking them up in the Catasto, and add one from the Catasto in the Tratte (or better still, check the lists of Surnames for both data sets to find an acceptable spelling).
2) The spelling of names has not been standardized between the Catasto and the Tratte (which has the more authoritative versions—there is also more information about names in the documentation for the Tratte than for the Catasto). You will have to guess at matches in the spelling of names between the two data sets. A match of the Gonfalone (Location in the Catasto; QUAR in the Tratte) may help you find the right person.
3) Many names and patronymics are missing from the Catasto data set. This is because David Herlihy did not code the names of subordinate family members listed in the tax declarations. For instance, the name of Cosimo [di] Giovanni de’ Medici is not present in the Catasto data set, although there are many records for him in the Tratte, because he was listed as a subordinate family member in the declaration of his father, Giovanni [di] Bicci de’ Medici in the Catasto. Of the 37,144 individual names that appeared in the original records of the Catasto for 1427, only 9,780 names of household heads (and only 36% of these had surnames) appear in the Catasto data set. Thus you will not find in the Catasto the names of many individuals who were living in 1427, although they may be present in the Tratte. But you might be able to surmise from patronymics available in the Tratte in which household an individual may have been living in the Catasto.