[talk-au] The Paradox of Postcodes (Was Re: Victorian Vicmap Address Import Proposal - Suburb and Postcode discussion)

stevea steveaOSM at softworkers.com
Thu Jun 17 06:04:10 UTC 2021


I know (I know), I’m talking to the Australia list and I’m in the USA (California).  I have friends from Oz, but I’ve never been (I’d love to visit as a tourist, it’s on my bucket list).

In the USA, the USPS (postal service) uses five-digit “ZIP” codes (Zone, digit 1; Improvement, digits 2 and 3; Plan, digits 4 and 5) for what you call postcodes, the five-digit version generally identifies a single post office, big or small.  Started in the 1960s (or so), they have grown to “ZIP+4” codes (nine digits) that seem to specify right down to a “side of a street on a block,” single apartment building, or even individual house level.  I believe there are even 11-digit versions (crawling right up yer bum, it seems; with 11 digits, even my cat could have his own ZIP code).  On the other hand, I have a Post Office box (identified by four digits) and the post office is identified by its five-digit ZIP code.  I once test-mailed an envelope to myself with just nine digits properly hyphenated (no name, no house number, no street, no city, no state), and sure enough, it arrived in my box.  (It had the usual "sprayed-on” zebra/barcode representing the ZIP+4 along the bottom to facilitate machine-reading further along the pipeline that all our other mail has, too, but was otherwise addressed with “only the ZIP+4”).

Three points about ZIP codes which might be similar to postcodes in Australia (and Canada and the UK, it seems):  despite what most people think, ZIP codes are NOT required for a letter to be delivered.  It might take a bit longer without one, but it WILL be delivered.  City, State, ZIP?  (Or ZIP+4?):  not really required, as City, State (only) does suffice.  Secondly, I’ve discerned (and had others who should know confirm) that a ZIP code is much like a “routing algorithm” (of 5, 9 or 11 digits):  it is NOT a geographic area that can be (easily) described by a polygon, even a multipolygon.  I mean, plenty of cartographic gymnastics have made geographic areas OUT OF ZIP codes (or postcodes) — some relatively “successfully” (accurately?) but they are not such things (a geographic area, even as they seem as though they are).

Finally, the whole thing about “these are the property of the post office and we’re going to be very non-sharing with them…” seems to be widespread with postcodes, I’m not sure why that is, but hey, if postal services want their codes to be proprietary, they can do that.  But that should make cartographers like us think twice about why we’re including them in a map:  what, exactly, can putting these data in OUR map “buy” us by doing so?  Yes, I know there is a general attitude of “postcodes are NEEDED, else how will the mail get delivered!” (thought in our mind’s voice approaching a shrill panic).  But, recall, (at least in the USA, maybe Australia, Canada, UK..., too) they aren’t strictly needed, but are more of a convenience for automation and the internal workings of how to sort and deliver mail, not really a function a map needs to provide its consumers (anyway).

Things to think about, and perhaps quite non-overlapping, but I felt like typing all that, so thanks for reading.


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