A UPRN gives every address a standardised format, enabling pseudonymised linkage to other sources of data. ASSIGN compares addresses in the NHS record with the Ordnance Survey's "Address Base Premium" UPRN database, one element at a time, and decides whether there is a match.

For example, the UPRN for 10 Downing Street is 100023336956, and that for Bristol Central Library is 000000199356. UPRNs, of up to 12 digits allocated by OS and local authorities, do not contain information about the location but identify records in the ONS UPRN Directory (ONSUD).