Then on July 1, 1963, the Post Office introduced the Zone Improvement Plan. The country was carved into 10 sections, 0 to 9. From there, 5-digit numbers (codes) were developed to identify each post office associated with an address. It was also the time that the two-letter state postal abbreviations were instituted.
I was fascinated as a kid by this. Just from the first digit in the ZIP Code, I knew where a letter came from. If it started with 0, it was from New England, New Jersey, US Virgin Islands, Puerto Rico and military addresses in the European theater; Guantanamo Bay, Cuba is 09360.
So, in New York State, 100-102 are Manhattan, 103 is Staten Island, 104 is the Bronx. 105 is suburban New York, with the places listed alphabetically, 106 is White Plains and so forth through 119, on the tip of Long Island. 120 and 121 are suburban Albany, 122 is Albany and 123 is Schenectady. Certain businesses or other institutions have their own ZIP Codes. 10048 is the zip code assigned to the former World Trade Center in New York City. The State University of New York in Albany is 12222, while the SUNY campus in Buffalo is 14222. ZIP Code 12345 is General Electric in Schenectady. And Spiegel is now ZIP Code 60609.
When I worked at a store in Albany in the 1980s, I decided to figure out where the orders for a horror film book was coming from. A decidedly large plurality of the requests, for some reason, were from 480 and 481, wealthy suburban Detroit.
In 1983, the US Postal Service began using an expanded ZIP Code called "ZIP+4." "A ZIP+4 code consists of the original five digit ZIP Code plus a four digit add-on code. The four digit add-on number identifies a geographic segment within the five digit delivery area, such as a city block, office building, individual high-volume receiver of mail, or any other unit that would aid efficient mail sorting and delivery." It is not mandated, but businesses use it often and there are savings to be had for bulk mailings.
On rare occasions, a place is assigned a ZIP code that does not match the rest of the state, e.g. the place is so remote that it is better served by a center in another state. "For example, Fishers Island, NY, which is off Long Island, NY, has ZIP code 06390 and is served from Connecticut, while all other New York ZIP codes begin with 1. Some Texas ZIP codes are served from New Mexico and have codes beginning with 8 rather than 7." And something I only discovered recently: "returned government parcels from the District of Columbia are sent to ZIP codes beginning with 569, so that returned parcels are security checked at a remote facility, put into place after after the anthrax scare."
The Census Bureau does not tabulate data by U.S. Postal Service ZIP Code. Instead, it created a new statistical entity called the ZIP Code Tabulation Area (ZCTA) to meet requests by data users for statistical data by ZIP Code. ZCTAs are close area approximations of USPS ZIP Codes service areas. For more information, go here.
Hey, you ABC Wednesday folks from outside the U.S.: how do YOUR postal postscripts work? I know that Canada has an alphanumeric system, and the first letter is roughly alphabetical from east to west across the provinces, with the territories last (X and Y). ROG