Long-form articles on how U.S. ZIP codes actually work — what each digit means, why some cities have hundreds of codes, how ZIP+4 came to be, and where the system causes real problems in insurance, sales tax, and everyday delivery.
Everything in one place: how the system works, what the digits mean, the four types of ZIP codes, and how to find the right one.
~7 min read
A digit-by-digit decoder with real examples — place any ZIP on a map of the U.S. without looking it up.
~6 min read
What those extra four digits mean, when they're required, and how USPS assigns them.
How a postal crisis after WWII led to Mr. ZIP, the digital age, and modern e-commerce.
Why ZIP codes don't line up with counties, cities, or school districts — and what they line up with instead.
A widespread misconception that creates real problems in research, insurance, and tax software.
~8 min read
Which metros top the list, why big cities need so many codes, and a deep dive on New York's 166 ZIPs.
From an IRS facility on Long Island (00501) to the Alaskan panhandle (99950), and the geography of the numbering.
The stories behind 90210, 12345, 20500, the White House, the CIA, and the highest-income ZIP in the country.
The parallel postal system that delivers mail to service members anywhere in the world at domestic postage rates.
~9 min read
Why your PO Box and your house can have different ZIPs, and how this trips up online forms.
Why the UK has alphanumeric codes, Japan has 7 digits, Hong Kong has none, and the U.S. has stayed at 5.
From auto premiums to homeowners coverage, ZIP codes are one of the biggest inputs in modern insurance pricing.
Why "ZIP code = tax rate" is one of the most expensive misconceptions in e-commerce, and how big sellers handle it.