ZIP Codes

Alice Goldfarb

ZIP Codes were designed for sorting letters and parcels, helping get the mail to the right delivery route as efficiently as possible.² Yet these identification codes are also deployed for other reasons. Along with cataloging place, ZIP Codes create space, with political and financial realities.

Introduced nearly sixty years ago, the Post Office Department introduced the Zone Improvement Plan (ZIP) Code to assist with mail delivery.³ Since then, ZIP Codes have come to act as a general designation about place, that is used by government, business, researchers, the general public, and other delivery services, while continuing to be a part of how the United States Postal Service (USPS) moves the 484.8 million mailpieces it delivers each day.⁴

The current ZIP Code consists of ten or eleven characters.⁶ As usually written, the first five are the ZIP Code as introduced in 1963, with the first three digits designating a general area and often a sorting facility, and the final two a local zone. When the ZIP + 4, launched in 1983, is used, the sixth character is always a hyphen, followed by two digits for a route and two for a side of the street. While the USPS may use an eleven digit code to ‘allow ordering by carrier-walking sequence,⁷ most people continue to use the original five digits and the post office adds granular information upon intake of the letter into the system.

The ZIP Code is often displayed in an even more machine readable way on an envelope, using the Postal Numeric Encoding Technique (POSTNET) or an Intelligent Mail barcode.⁸ The code itself is displayed through height-modulated pseudo-binary four-state bars.

For example, using POSTNET, 123 would be displayed as 

with each of the digits shown via five bars, ascending (tall) as the 1 and track (short) as the 0 for a binary code. Intelligent Mail barcodes includes information besides the ZIP Code, indicating the sender and delivery point. Inclusion of the barcode is required for some types of bulk mailings, because it allows for automation in the sorting process. For mail without a barcode, a postal service machine or person reads the address and ZIP Code and adds a printed barcode to the envelope or package.

The Post Office Departement, the precursor to the USPS, promoted the merits of ZIP Codes with the character Mr. ZIP. Appearing in cartoons and on promotional materials, Mr. Zip spent the 1960s reminding  individuals, and more importantly business, to incorporate ZIP Codes into their addressing practices. “We fully expect Mr. Zip to become as familiar a figure as the Agriculture Department’s Smokey Bear,”¹¹ suggested an overly optimistic Post Office Department publication. Now retired to museum exhibits, Mr. Zip’s encouragement emphasized that the new system needed to have widespread adoption to succeed.

Although Mr. Zip may be retired, the use of the ZIP Code has spread far beyond use in postal sorting. While many of us think of a ZIP Code as being synonymous with a place, it is actually the description of a delivery path. A street might be served by more than one delivery route, or some buildings might be served by a different ZIP Code than their neighbors. In rural areas, residents of one town may have mail delivered from the post office of another. However, the understanding of ZIP Code as place prevails, from using the numbers as a shorthand for a location (90210), searching in an online map, or having insurance rates and housing access based on your mailing address.¹² For example, the New York City Department of Health defines neighborhoods by ZIP Code,¹³ rather than by major roads or other distinguishing geography, thereby making decisions or allocating available resources based on postal logistics rather than public health decisions. The accumulation of data that is now identified by ZIP Code makes it less likely that the Census, or anyone else, will move away from this identification. Continuing to use the system means carrying along past understandings of a place, whether as high-crime or highly desirable.

“The Untold Story of the ZIP Code,” a 2013 document from the USPS Office of the Inspector General, discusses possible updates to the system , including allowing for dynamic routing depending on the mail load for a particular day.¹⁴ While other organizations such as what3words¹⁵ and Google’s plus codes¹⁶, have established their own location designation codes, the ZIP Code continues to be in widespread use inside and outside the postal system. Its ubiquity adds to its usefulness. If I am looking up information about a place, I am more likely to know the ZIP Code than what county it is in, even if the information was gathered by county. The ZIP Code’s frequent use reinforces its importance.

The ZIP Code was created as part of bringing postal delivery into a more mechanized future, increasing efficiency and getting the mail delivered with fewer humans handling it. Since then, it has come to be understood as an areal identifier. With this categorization has come a general notion of place as quantifiable, flattening the understanding of neighborhoods into numbers, functional operations whose consequences were likely never considered by the Post Office Department a hundred years ago.

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1. “Mr. ZIP and the 5 Little Digits,” GPO, O-733-400, 1964. From “Mr. Zip Around Town and in Local Post Offices,” Smithsonian National Postal Museum. https://postalmuseum.si.edu/exhibitions/flashing-across-the-country/mr-zip-around-town-and-in-local-post-offices. Accessed 21 February 2020.
2.  “The Untold Story of the ZIP Code,” U.S. Postal Service Office of Inspector General. RARC-WP-13-006, April 1, 2013, i.
3.  ibid.
4. “One Day In The Life Of The U.S. Postal Service,” USPS. https://facts.usps.com/one-day/#fact49. Retrieved 20 February 2020.
5. “Mail Moves the Country, ZIP Code Moves the Mail,” Post Office Department, 1968. From “Mr. Zip as a Pop Icon,” Smithsonian National Postal Museum. https://postalmuseum.si.edu/exhibitions/flashing-across-the-country/mr-zip-as-a-pop-icon. Accessed 20 February 2020.
6. “The Untold Story of the ZIP Code,” U.S. Postal Service Office of Inspector General. RARC-WP-13-006, April 1, 2013, iii.
7. “The Untold Story of the ZIP Code,” U.S. Postal Service Office of Inspector General. RARC-WP-13-006, April 1, 2013, 6.
8. “Intelligent Mail® Barcode Questions & Answers,” USPS, Intelligent Mail® Barcode FAQs. 1 September 2008. https://postalpro.usps.com/storages/2016-12/217_USPSIMB-QandA.pdf. Accessed 21 February 2020.
9. Decoder/Encoder. USPS PostalPro. https://postalpro.usps.com/ppro-tools/encoder-decoder. Accessed 21 February 2020.
10. “How USPS Sorts Mail,” Insider. https://youtu.be/gB7QOK1bd3U
11. “Localized Feature for Cities Already Zoned,” United States Post Office Department, 1963, Files of the Third Assistant to the Postmaster General Files, folder 03-03-08, Smithsonian National Postal Museum Library.
12. “The Tyranny of the ZIP Code,” Anna Clark. The New Republic, 8 March 2013. https://newrepublic.com/article/112558/zip-code-history-how-they-define-us. Accessed 21 February 2020.
13. “ZIP Code Definitions of New York City Neighborhoods”, New York State Department of Health. https://www.health.ny.gov/statistics/cancer/registry/appendix/neighborhoods.htm. Retrieved 20 February 2020.
14. “The Untold Story of the ZIP Code,” U.S. Postal Service Office of Inspector General. RARC-WP-13-006, April 1, 2013, i.
15. “Addressing the world,” what3words. https://what3words.com. Retrieved 20 February 2020.
16. “Addresses for Everyone,” plus codes. https://plus.codes. Retrieved 20 February 2020.