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A 5-Digit ZIP code represents a USPS delivery area. A 9-Digit ZIP code, also known as a ZIP+4 code or an extended ZIP code, includes the same information as the 5-Digit ZIP code, plus additional information about a specific delivery route within the delivery area.

Data scientists should know that ZIP codes do not always fall within state boundaries (or even of the borders of states within a zone). There are over 100 cases where ZIP codes cross state lines.

If the ZIP code does not match with the ZIP code the card-issuing bank has on file in the processing system, the merchant can choose to decline the transaction and take appropriate steps to ensure the card is not being used fraudulently.

Usually what happens is a carrier or post master from the office where the package is sent will correct the zip code by looking at the address and even reach out to that particular post office to ensure the package is delivered to the correct address.

So what do the extra numbers mean? These last 4 digits represent specific delivery routes within delivery areas. This extra detail means an even more precise matching to a more granular level. It could represent a handful of houses on one side of a street, or even a single building that receives a high volume of mail.

The standard ZIP code notation used by the United States Postal service uses five digits to identify a delivery area. An example of a standard US ZIP code is 90210.

A wrong zip code can result in a package being shipped to the wrong state, or getting left at the wrong address because of a familiar street name in another zip code. It even helps to make sure the zip code is larger so it stands out more. This makes the sorting process faster and easier for the carrier.