The encyclopedia · Engineering & Operations · Operational decision · 1943-1963
The ZIP code turned a full address into five digits a sorter could read
The US Post Office compressed a whole address into a number so mail could be sped up and later sorted by machine.
United States Post Office Department
the move
By the 1960s the United States was sending more mail than its Post Offices could sort by hand, and the shortage of experienced sorters worsened during the Second World War when workers went to the front. Postal zone codes existed in the largest cities from 1943, giving delivery districts a one- or two-digit number, but growth called for something smarter.
The Post Office Department introduced the Zoning Improvement Plan Codes — ZIP Codes — in July 1963. A five-digit ZIP packed the destination into a small number: the first digit the broad geographic region, the following two the mail centre in that region, and the last two the specific post office or delivery zone. In 97403, for instance, the 9 meant the West Coast and Pacific area, the 74 the Eugene, Oregon mail centre, and the 03 the University of Oregon.
The point was that a sorter no longer needed a clerk's full knowledge of the country. Sorting became the reading of five digits, which a human could do quickly and accurately, and which a machine could be built to do. The Post Office promoted it with Mr ZIP, a cartoon mascot, and celebrities like Ethel Merman singing a ZIP-code jingle.
The five-digit code became the backbone of later automation and of all postal addressing in the US, and the same idea — turn an address into a compact standard key — spread to every postal system that could then machine-sort its mail.
why it works
- A town-and-street address demanded knowledge that only a veteran sorter had
- Five digits compress region, centre and delivery zone into machine-readable form
- Sorting faster by hand meant the code had to be short and fixed
- A standard key was the precondition for any later automated sorting
what transfers
To make a slow human task automatable, first compress the information into a fixed, simple code that a machine can read and sort on.
what came after
ZIP codes were assigned to every US address by 1963 and became the basis of machine mail sorting and of the next generation of delivery technology, from POSTNET barcodes to the intelligent mail barcode. The same five-digit standard shaped address databases in marketing, logistics and mapping, and remains the reference key for US addresses decades later.
references
spotted an error? The archive wants to know.