To do this, they sectioned bunches of addresses into census blocks.
They've compiled a list of cartographic boundaries since ZIP codes are "convenient" to work with. That's more the job of the census bureau. but the USPS' job was to design efficient carrier routes, not partition the population into coordinate regions so much. They vary widely and are actually quite un-helpful unless you're delivering mail or packages.
But since each ZIP code is a different size, it's really hard to tell what actual distances you're talking.Ī 9-digit ZIP code might be portioned to a floor of a building, so there you have overlapping ZIP codes for potentially hundreds of addresses.īottom line: ZIP codes don't, contrary to popular belief, provide geographical or boundary data. 7- and 9-digit ZIP codes are the most specific, often down to block or neighborhood-level in urban areas. 5-digit ZIP codes are the least "precise" (though the term "specific" might be more meaningful here, since ZIP codes don't pinpoint anything). Military addresses are an entirely different class of addresses using the same namespace. Certain naval ships have their own ZIP codes. This is because even though Schenectady contains 12345, where the address is "valid," it geometrically intersects with the "real" ZIP codes for Schenectady. Now, try the same bogus address, but without a ZIP code, and instead do the city/state: Many universities function in a similar manner. Pretty much anything internal to the ZIP code is irrelevant to the USPS, including the street address (technically "delivery line 1"). it's VALID! Why? The USPS will deliver a piece to the receptacle for that unique ZIP code, but at that point, it's up to GE to distribute it. When you try to verify that, notice that. Head over to SmartyStreets and punch in a bogus address in 12345, like: Just for fun, let's try verifying an address in a unique ZIP code. While most US ZIP codes used to show a region on Google Maps, these types cannot because the USPS does not "own" them, so to speak, and they have no area.) (Edit: In a previous version of Google Maps, when you follow that link, you'd notice that the placement marker was hovering, because it points to a ZIP code, which is not a coordinate. For instance, the ZIP code "12345" belongs to General Electric up in Schenectady, NY. Companies and universities frequently get their own ZIP codes for marketing or organizational purposes. Some of these - among others - are "unique" ZIPs. Some 5-digit ZIP codes are only a single building, or a complex of buildings, or even a single floor of a building (yes, multiple zip codes can be at a single coordinate because their delivery points are layered vertically). Addresses are not allotted based on geography, but on the routes that carriers travel which usually relates to streets and travelability. What is this "abstract space of USPS-designated addresses"? That's how I am describing the large and mysterious database of deliverable locations maintained by the US Postal Service. What you will find, though, is that they appear to be geographically oriented because it would be inefficient for carriers to have a route completely irrelevant of distance and location.
They are not correlated to geographical coordinates. Just as lines are strings of points along a coordinate plane, ZIP code lines are strings of delivery points in the abstract space of USPS-designated addresses. In actuality, ZIP codes are lines which represent, in a sense, mail carrier routes. We often think of ZIP codes as areas (polygons) because we say, "Oh, I live in this ZIP code." which gives the impression of a containing region, and maybe the fact that ZIP stands for " Zone Improvement Plan" helps the false association with polygons. An elaboration of my comment, that ZIP codes are not polygons.