Our proprietary process builds the ZIP Plus 4 Database Premium Plus Centroids product from raw USPS ZIP+4 data by geocoding the ZIP+4 address ranges against parcel points and street segments to find precise ZIP+4 centroids. The ZIP+4 ranges are then expanded, producing a complete set of over 60 million records. PO Box ZIP+4s are initially represented by the USPS as a low value and a high value (e.g., 20001-0001 to 20001-0486). We extend these ranges to represent the individual ZIP+4 values included within the ZIP+4 range.
Finally, we implement a rigorous quality control process to ensure the ZIP+4 product is of the highest quality. This includes removing any duplicate ZIP+4 values, as well as ensuring attribute and positional accuracy.
ZIP Plus 4 Database Premium Plus Centroids now includes ZIP Code centroids for ZIP Codes which do not have any corresponding +4 records. This allows additional unique ZIP Codes to be included as unmatched Z4 records to enhance match rates and correspond to ZIP Code-level data.