Is there a unit smaller than the ZIP Code?
Yes. To aid in mail delivery, the USPS divides ZIP Codes into carrier routes. As the phrase implies, these are determined as the actual physical area an individual mail person can cover every day. Carrier routes always sync within their corresponding ZIP Code. The deepest discounts the USPS gives people conducting direct mail campaigns are to those people who mail by carrier route, in which case carrier route maps may be helpful.
