ZIP +4

Maybe this has already been discussed, but about how did they determine which numbers defined any particular city in a regular (5 digit) ZIP code. I mean does the number and position have any particular meaning? Also, exactly how far do the extra 4 digits in the ZIP + 4 narrow it down (my house, street, block, etc.)?

Well, I don’t know about US codes, but in the UK postcodes are either six or seven characters in two groups (e.g. GU14 6AQ or NW5 3QE). The first letter characters signify the postal area - e.g. GU is Guildford in Surrey. The only exception is London, which has codes based on comnpass direction - e.g. NW5 is North West of the centre, EC is East Centre and so on.

I worked for a little while at the Post Office on a project for tracking parcel deliveries which involved postcodes a lot, and in the UK at least a postcode can identify an address to within 6 houses.

The original intention was for a postcode to narrow an address down to 100 residences, but in reality it is possible to address a letter with the number and street name and postcode and it will get there nearly every time.

[ X marks the spot ]

I think they worked pretty much from northeast to the west, with some priority to NYC that had zone numbers that, I think, turned into part of the zip code. If I’m not mistaken, the 4 extra digits basically narrow it down to the block, but there may be exceptions to that, like outside a city and such. But, here in a relatively small city, it translates to a block.

The 1st digit is the region of the US. The next two are the sectional center (the main distributing PO for the whole area.) Well they’ve changed the terminology but I forget to what. There’s sort of a pattern to how those two digits are arranged but I’ve never worked it all out. The last two are arranged alphabetically within your area (or started out that way.)

The last four are unique to P.O boxes and important businesses. The rest of us share with neighbors. How many depends on exactly how they implemented the system in your particular area. (The same general system was used across the U.S. but there are minor variations.) Your 7th and 8th digit are for your portion of the PO area (or it started out that way.) The last two digits generally narrow it down to one side of your block but that differs from here to there. For cities, that would be some portion of an apartment building.

I wonder: How does the +4 zip codes translate to a situation that is in place in several locations in New York City: That is, where a single building will have a zip code all it’s own? IIRC, there are at least a dozen or more in NYC that fit this description, and I assume other larger cities/buildings have the same issues.

I mean, is the building also the same +4 as well? Or can you just look at the +4 without any other information and say, “Ah! This goes to the fourth floor,” or even more exact?

Yer pal,

I tried out that technique. I used 1 World Trade Center as an example (it’s 10048). When I looked on the USPS website, the +4 codes were sort of bunched together that offices on a certain floor started with those two digits.
(E.g. A company on the 21st floor would be 10048-21XX). It doesn’t hold true for every office in the building however. I would imagine that new offices created out of reconfigured older ones may screw up the system.

For several years I handled bulk mailings for a small state agency, and was responsible for ensuring we had ZIP+4 as accurate as possible. The zip codes are assigned as people noted above: there are something like 450 “sectional centers” in the country, grouped in 10 large more-or-less geographic blocks (the first digit). Each “sectional center” has between one and four three digit codes for their area, and the communities are numbered in alphabetical order within the area that sectional center covers. (Exception: where only one three-digit code is assigned to an area, the first few numbers are for the city where the sectional center is located.) For example, the center at Syracuse, NY services post offices with 130xx, 131xx, and 132xx zip codes. Post offices within Syracuse (and a couple of suburbs) get 132xx zip codes. The other towns and villages are in alphabetical order starting with 13001 for a town I don’t remember that begins with Ac… and ending with 13167 in West Monroe (there may be something after that I don’t know about). In Watertown NY, which has the 136xx series, Watertown is 13601, Fort Drum (army base served from Watertown) is 13602 and 13603, and Adams is 13605, Adams Center 13606, running up to Woodville at 13698. As I remember, 0xxxx is New England, New Jersey, and APO and FPOs operating out of New York City, 1xxxx is New York and Pennsylvania, 2xxxx is Maryland, Delaware, WVa, Virginia, and NC, and so on, going down the East Coast, then the Midwest, Great Plains, Texas, Mountains, California, Northwest, Hawaii, and Alaska.

ZIP+4 codes are assigned by the individual post offices. In multi-ZIP-code cities, a single ZIP code may cover 9,000+ P.O. boxes and nothing else. (13201 in Syracuse does just this.) Some general rules:

-9998 is the Postmaster for that P.O.
-9999 is General Delivery.

In smaller communities (under 50,000 or so)Post Office Boxes are usually the low-numbered codes, with leading zeroes to make a four-digit number, so PO Box 1 is -0001 and PO Box 375 is -0375.

If the post office services rural routes, they are usually numbered as follows:
-9801 is RR 1, rural box unknown
-9802 is RR 2, same (and so on)
-97xx are assigned to RR 1
-96xx are assigned to RR 2
and so on, counting down as the RR number goes up.

As rural “street” addresses are implemented to replace this (you used to be at RR 1, Box 93, but are now 7501 Old Duckburg Road), these numbers are being phased out and replaced with numbers in the range -5000 to -8999.

Streets are -1xxx and up, with -1000 usually being the first block of the main downtown street, and -6998 being somewhere out in the 'burbs just shy of where the rural routes start.

Most businesses, associations, government agencies, and so on have their own ZIP+4 number, over and above what they would have through their physical location.

As noted by others, big cities with larger buildings are a law unto themselves, and will often have a bunch of zip codes assigned to specific heavy-mail locations. For example, Albany NY has about 20 ZIP codes specifically assigned to State agencies, Dept. of State being 12231 for example. The New York State Senate has 12247, and adopted the useful breakdown of assigning the 61 Senators an individual ZIP+4 matching their district with a leading -09, so that Sen. Ray Meier of the 47th District is 12247-0947.

We now live in a small crossroads community (Pilot) serviced by a rural route from a nearby town (Zebulon), with -59xx being used for the area around Pilot, so our friends 1/2 mile down the road are at -5911 and our own +4 code is -5936, both appended to Zebulon’s 27597. Presumably whoever has PO Box 1 in Zebulon is 27597-0001 and the Postmaster definitely can be reached at 27597-9998.

More than anybody wanted to know, I’m sure, but I hope it’s some help.

This is fun. As alluded to above, they are running out of numbers in areas where they did not correctly predict growth so are adding out of sequence numbers – which do not bother the computers.

As Polycarp said, businesses are given unique codes outside the grid system. Those cause the USPS’s own software to often supply the wrong ZIP+4 (by location rather than company.) Ha.

Also, exactly how far do the extra 4 digits in the ZIP + 4 narrow it down (my house, street, block, etc.)?

The extra four digits, for residential purposes, narrows it down to; the first two digits determine the segment address, the last two determine the sequence order.
There are four possible addresses per segment, in this case. These are not particularly identifiable by the actual number, but by the bar code, which actually contains the other 1 thru four sequence order.
You don’t see the whole thing, unless you have a reader to translate the bar code, but the machine reads it.

Anyway, the +four numbers show, which part of a block, of a particular street, and one of four possible street addresses, for that part.
A bar code sorter can then put the piece in the exact correct order, but a human can only determine, that it is one of four possible addresses.
(without consulting the bar code database)

I just got ready to mail off a payment to the IRS (don’t ask), and I noticed the address they had for me was zip code + 7. Or zip code plus 4 and 3 extras. By that I mean, the zip code and +4 parts were the same as usual, but there were 3 more digits. So, maybe things are expanding as we speak, kinda like the universe, or maybe not.

Jim: maybe you are right about the IRS and the universe being related. After all, Chaotic Theory is a big thing for the universe.

A few years ago, the USPS was using an additional two (after the nine) digits to give each location a unique number (which ZIP+4 didn’t do, except in the sticks or PO boxes.) They do not seem to have made any move towards getting us to use more than the ZIP+4. The extra digit beyond those two is a new one on me. Why do they bother? The USPS will implode in a couple more years and e-mail will completely and utterly replace them.

well, i just checked out and found that you can look up yer zip+4, which i knew what mine was anyway, but it also gave a delivery point (05) and a check digit (2)

could this be the zip+4 +3 ?