ZIP+4 - the last four digits in ZIP+4. The addition four digits more precisely pinpoint the final destination. Larger mail volumes, increasing numbers of delivery addresses, and the adoption of automated machinery made ZIP+4 a necessity in 1983.
Zone Systems - a means of organizing mail using a zoning address system of one or two numbers in the hundred twenty-four largest post offices. Individuals added the zone code between the city and state, such as New York 4, New York. The numbers represented the post office or sub-post office closest to the final delivery address.