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To get a rough idea of how often a ZIP-9 narrows things down to a single street address, I took a look at the sales tax rate and boundary files made available for states that are in the Streamlined Sales Tax Agreement [1]. 12 of those states, Arkansas, Georgia, Iowa, Kansas, Nebraska, North Carolina, Ohio, Oklahoma, South Dakota, Tennessee, Vermont, and Washington, use address-based tax rates. (The other 12 either just have one rate for the whole state, or just go by ZIP). For each ZIP-9 in the address files for the 12 address-based states, I found the lowest and the highest street number for that ZIP-9. I then counted how many of the ZIP-9s had the lowest street number the same as the highest street number. There were a total of 9,311,327 distinct ZIP-9 values. 2,415,305 of them had a low to high range that only included one number. That's about 26% of the ZIP-9's having a unique street number. Note that this does not necessarily mean a single household, because I'm not looking at the full address. Apartment buildings, for instance, will in many cases show up in that 26%. [1] https://www.streamlinedsalestax.org/Shared-Pages/rate-and-bo... |