Zip Codes

[COLORADOrk]

What two zip codes that border each other have the largest difference in number? This shouldn't be too hard to figure out.

[CNGL-Leudimin]

At first glance it has to be somewhere along the Mississippi/Louisiana border, as those have the greatest difference between their ranges.

Of course, the thread title already implies it's the USA, due to the unique name they give to postcodes. Otherwise I would have come up with 04110 and 84750 in France .

[1995hoo]

^^^^^

Remember the US government loves its acronyms. "ZIP" in "ZIP Code" is an acronym that stands for "Zone Improvement Program." That name had the happy coincidence of shortening to a word that connotes speed, as in faster mail delivery, so the term stuck.

I've sometimes wondered whether addressing something the old way (e.g., "Brooklyn 9, NY" instead of 11209) would work, but I've never bothered to try it to find out.

[Dirt Roads]

For West Virginia, the winner is Henderson (25106), which is across the river from the huge Gallipolis zip code zone (45631) giving a difference of 20,525.  If you look at the map, it doesn't look like the Henderson zip code actually touches the Ohio River (but we all know that the town of Henderson is located at the confluence of the Kanawha and Ohio rivers).  All of the town proper is in the 25106 zip code, plus there's a tiny sliver of land along the Kanawha with a few houses that connect to main zip code area just west of the town of Southside.  Otherwise, the rest of that area has a 25515 zip code (Gallipolis Ferry). 

How about a double whammy:  Chester (26034) is adjacent to East Liverpool, Ohio (43920) and Georgetown, Pennsylvania (15043).  The differences are 17,886 and 10,991.

[NWI_Irish96]

Largest I can find in Indiana is Mount Vernon's 47620 touching the 62984 of Shawneetown, IL, at the mouth of the Wabash River.

[zachary_amaryllis]

without really searching this out, i would say somewhere along the montana/wyoming border

montana is all 59xxx, and wyoming is (i think) 82xxx

[SkyPesos]

Looking at a Zip codes map, there's three places where crossing state lines would have a difference of at least 20001

- Ohio (4) and Pennsylvania (1)
- Montana (5) and Wyoming/Idaho (8)
- Arkansas/Louisiana (7) and Tennessee/Mississippi (3)

[Dirt Roads]

For West Virginia, the winner is Henderson (25106), which is across the river from the huge Gallipolis zip code zone (45631) giving a difference of 20,525.  If you look at the map, it doesn't look like the Henderson zip code actually touches the Ohio River (but we all know that the town of Henderson is located at the confluence of the Kanawha and Ohio rivers).  All of the town proper is in the 25106 zip code, plus there's a tiny sliver of land along the Kanawha with a few houses that connect to main zip code area just west of the town of Southside.  Otherwise, the rest of that area has a 25515 zip code (Gallipolis Ferry). 

How about a double whammy:  Chester (26034) is adjacent to East Liverpool, Ohio (43920) and Georgetown, Pennsylvania (15043).  The differences are 17,886 and 10,991.

- Ohio (4) and Pennsylvania (1)

Wow! I didn't pay any attention but the two I've mentioned also touch each other:  East Liverpool, Ohio (43920) and Georgetown, Pennsylvania (15043) have a difference of 28,877.  Just north of there the numbers flip to 16XXX versus 44XXX, so Bessemer, Pennsylvania (16112) and Petersburg, Ohio (44454) have a difference of 28,342.  Fun fact:  Petersburg also touches the tiny ethnic borough of S.N.J.P., Pennsylvania (part of zip code 16120).  That abbreviation stands for Slovenska Narodna Podporna Jednota, the fraternal society whose members make up the population.

[CtrlAltDel]

^^^^^

"ZIP" in "ZIP Code" is an acronym that stands for "Zone Improvement Program." That name had the happy coincidence of shortening to a word that connotes speed, as in faster mail delivery, so the term stuck.

I don't think it was a coincidence at all, if for no other reason that the expression "zone improvement plan" doesn't really make sense. I mean, you don't really improve a zone by giving it a number.

[CNGL-Leudimin]

I now believe the highest differences may be along the Mississippi/Arkansas border. Crossing the Mississippi river on US 49 means a jump of 33,716 between Dundee, MS's 38626 and Helena (part of Helena West Helena), AR's 72342. Of course, that using only postcodes that get called "ZIP codes", the French example I posted above is over 80,000; courtesy of France numbering their departments by alphabetical order and no. 04 (Alpes de Haute Provence) bordering no. 84 (Vaucluse).

[1995hoo]

^^^^^

"ZIP" in "ZIP Code" is an acronym that stands for "Zone Improvement Program." That name had the happy coincidence of shortening to a word that connotes speed, as in faster mail delivery, so the term stuck.

I don't think it was a coincidence at all, if for no other reason that the expression "zone improvement plan" doesn't really make sense. I mean, you don't really improve a zone by giving it a number.

Well, it certainly wasn't a "coincidence" that they chose a catchy name for marketing purposes in conveying it to the public. Insofar as the system "improved" on their ability to process mail quickly using the existing postal "zones," though, I suppose the name makes sense. As seen in the example in my prior post, some large cities were divided into "postal zones" to help with processing mail there by routing it to the appropriate post office within the larger area. The ZIP Code system expands that to the country as a whole. I've never bothered to find out what the additional four digits after the hyphen mean, though I know what the full ZIP+4 is for our house and my mom's house.

I now believe the highest differences may be along the Mississippi/Arkansas border. Crossing the Mississippi river on US 49 means a jump of 33,716 between Dundee, MS's 38626 and Helena (part of Helena West Helena), AR's 72342. Of course, that using only postcodes that get called "ZIP codes", the French example I posted above is over 80,000; courtesy of France numbering their departments by alphabetical order and no. 04 (Alpes de Haute Provence) bordering no. 84 (Vaucluse).

That seems highly likely to be correct:

[Scott5114]

I've never bothered to find out what the additional four digits after the hyphen mean, though I know what the full ZIP+4 is for our house and my mom's house.

They are, as you might expect, more precise subdivisions of a zip code for sorting use. There's even an additional two digit "delivery point code" (DPC) that can be appended to the ZIP+4 (making 11 digits in total) that uniquely identifies a single mailbox. (You can sometimes find this code printed across the bottom of your mail at the time of postmarking, along with a barcode that does the actual heavy lifting when it comes to sorting.) This seems to imply that each ZIP+4 code can only contain 100 mailboxes, and thus each ZIP code can only contain 1,000,000 mailboxes.

In ZIP codes that are solely reserved for PO Box use, ZIP+4 codes normally simply mirror the PO Box number. For example, my business address is P.O. Box 1428 in Norman 73070 (which only contains PO Boxes, no actual physical addresses), so my ZIP+4 there is 73070-1428. (I assume since the DPC is not needed in this case, it's always 00 or 01 or something like that. I'll have to keep an eye out and see if this code ever gets printed on my mail.)

[CtrlAltDel]

In ZIP codes that are solely reserved for PO Box use, ZIP+4 codes normally simply mirror the PO Box number. For example, my business address is P.O. Box 1428 in Norman 73070 (which only contains PO Boxes, no actual physical addresses), so my ZIP+4 there is 73070-1428. (I assume since the DPC is not needed in this case, it's always 00 or 01 or something like that. I'll have to keep an eye out and see if this code ever gets printed on my mail.)

The delivery point code for the post office box in question is 28. You can find it with the Post Office's ZIP Code lookup form.

[Scott5114]

Interesting. I knew about that tool but never noticed the drop-down that displays the DPC. It would seem like the DPC is directly derived from the building number in most cases (P.O. Box 1428 = DPC 28, my house has street address xx29 and the DPC is 29, my parents' house has street address xx06 and the DPC is 06). I wonder if that varies in cases where there are two nearby parallel streets that have the same house numbers, or if the ZIP+4 boundaries are drawn in such a way that this is impossible.

[CtrlAltDel]

Interesting. I knew about that tool but never noticed the drop-down that displays the DPC. It would seem like the DPC is directly derived from the building number in most cases (P.O. Box 1428 = DPC 28, my house has street address xx29 and the DPC is 29, my parents' house has street address xx06 and the DPC is 06). I wonder if that varies in cases where there are two nearby parallel streets that have the same house numbers, or if the ZIP+4 boundaries are drawn in such a way that this is impossible.

In most areas with single-family residences, the +4 code refers to one side of a street one block long. So the even number side of the 500 block will have have one +4 code, and the odd side will have another (most often varying by 1), and then the 600 block will have two more +4 codes, and so on. In other areas, the +4 codes can refer to smaller areas, sometimes a single building.

So, with the +4 code and the last two digits of the address, you pretty much get a single house. An apartment building will often have its own +4 code with the apartment number being the the delivery point. There's also a system if the apartments are lettered instead of numbered. Post office boxes have another system, based on the box number, as you've seen.

[Scott5114]

Very cool, thanks for the information.

I got curious how non-integer addresses are handled, so I popped in this pair of mailboxes. The lookup tool accepts both 511 and 511 1/2 as valid, but returns both of them as 73071-5243 11. I was expecting 511½ to get some arbitrary code, such as perhaps 99, as building numbers in Norman very rarely have high numbers in the tens place, but it would appear that's not the case. (GSV history does show the installation of the 511½ box as occurring sometime in either 2018 or 2019, though, so it's possible that whatever database the lookup tool runs on simply doesn't include it.)

[CtrlAltDel]

Very cool, thanks for the information.

I got curious how non-integer addresses are handled, so I popped in this pair of mailboxes. The lookup tool accepts both 511 and 511 1/2 as valid, but returns both of them as 73071-5243 11. I was expecting 511½ to get some arbitrary code, such as perhaps 99, as building numbers in Norman very rarely have high numbers in the tens place, but it would appear that's not the case. (GSV history does show the installation of the 511½ box as occurring sometime in either 2018 or 2019, though, so it's possible that whatever database the lookup tool runs on simply doesn't include it.)

That annoys me, too, but I think the idea is to keep things in numerical order.

For everything you want to know, look up 2458_CASLTR97.PDF on Google.

[Scott5114]

↑ Neat find. Guessing you must have reason to deal with DPCs fairly often if you just know that PDF exists offhand.

Looks like the official policy is to just ignore any fraction in computing the DPC, so 511 and 511½ both having a code of 11 is correct. I suppose the mail for both boxes is sorted together and the mail carrier is responsible for sorting individual mailpieces and putting them in the correct box at delivery time. I hope the boxes are owned by either the same person, or people who get along well, because I would imagine mix-ups happen pretty frequently (the mail carriers in this part of Norman take an...avant-garde approach to deciding which mail goes in which box sometimes, especially under the current postmaster general).

I suppose the real question is why that box was assigned 511½ in the first place. The propane business next door is 523, so it shouldn't have been a problem for the 511½ box to be assigned the number 513 (and thus a DPC of 13).

[GaryV]

My Plus 4 is 4223, DPC 04, which matches the last 2 digits of my address.

The house across the street has Plus 4 of 4222, DPC 05.

The address that is 100 greater than mine, but still on the same block, has a different Plus 4 of 4270, but again the DPC 04 matches the last 2 digits of the address.

[NWI_Irish96]

↑ Neat find. Guessing you must have reason to deal with DPCs fairly often if you just know that PDF exists offhand.

Looks like the official policy is to just ignore any fraction in computing the DPC, so 511 and 511½ both having a code of 11 is correct. I suppose the mail for both boxes is sorted together and the mail carrier is responsible for sorting individual mailpieces and putting them in the correct box at delivery time. I hope the boxes are owned by either the same person, or people who get along well, because I would imagine mix-ups happen pretty frequently (the mail carriers in this part of Norman take an...avant-garde approach to deciding which mail goes in which box sometimes, especially under the current postmaster general).

I suppose the real question is why that box was assigned 511½ in the first place. The propane business next door is 523, so it shouldn't have been a problem for the 511½ box to be assigned the number 513 (and thus a DPC of 13).

Addresses are assigned by cities/counties and not by the USPS, and they likely don't know or don't care that ½ in an address might cause issues.

[chrisdiaz]

I couldn't find any information for this online. To me, it seems odd that the majority of Georgia's ZIP codes start with 30 and 31, but there are some in the Albany area that start with 398.

[Scott5114]

I couldn't find any information for this online. To me, it seems odd that the majority of Georgia's ZIP codes start with 30 and 31, but there are some in the Albany area that start with 398.

The first three digits of a ZIP code correspond to the sorting center that serves that ZIP code. Sorting centers 300-319 are all in Georgia, and then 320-349 are all Florida (except 340). My guess is that the Albany 398 sorting center was simply established after all of the other Georgia centers, so they had to skip to a higher number since 320 was already in use in Florida.

Wikipedia has a chart of these: https://en.wikipedia.org/wiki/List_of_ZIP_Code_prefixes

[KEVIN_224]

Always thought it was weird how two or three towns in York County, Maine are 039XX while the other 98% or so of Maine is all 04XXX. I used to live in Wells (04090) and Old Orchard Beach (04064).

[Molandfreak]

Mexico also has 5-digit postal codes, so maybe it could be somewhere along the border if you include those.

[Molandfreak]

https://worldpostalcode.com/mexico/

Zip code 92283 borders postal code 21000 east of Mexicali.