This is what USPS tried to solve with the ZIP+4 mechanism. ZIP codes, as is widely known, are almost always at least a semi-large grouping of streets (excludin

This is what USPS tried to solve with the ZIP+4 mechanism. ZIP codes, as is widely known, are almost always at least a semi-large grouping of streets (excluding custom-assigned ZIP codes for a building that gets a lot of mail and other non-standard codes). Adding four digits on the end for a "standardized address" means that a specific block and, often, a subset of numbers on that block, can be identified. For example, ZIP code 90210 covers the bulk of Beverly Hills, California but 90210-5317 narrows it down to just the odd numbers of the 200 block of South Beverly Drive or, according to the USPS database, a maximum possibility of 23 delivery addresses (because not all of the numbers in that block block are assigned).