| ▲ | mixdup 3 days ago |
| zip codes are not geographic areas, they are a collection of mail delivery points. Sometimes those points are not geographically contiguous or may overlap |
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| ▲ | paulsmith 3 days ago | parent | next [-] |
| This is a fact of ZIP Codes that a lot of people stumble one. I've worked on GIS/mapping projects in the past where stakeholders wanted or assumed ZIP Codes to be polygons. Another complexity that surprises folks is you can't guarantee a one-to-many state-to-ZIP Code relationship. There are several (I forgot offhand how many, I used to have them memorized) that span across state boundaries. |
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| ▲ | y-c-o-m-b 3 days ago | parent [-] | | Yep, this fact eluded me earlier in the year. I was supposed to map out all ZIP codes in the US and color their boundaries based on certain stats we had. We were surprised to find many areas in the US were empty because they didn't have ZIP codes. I did a quick search and found out ZIP codes are driven by mail routes, and that instantly made sense to me, but the product stakeholders were very surprised to learn it. | | |
| ▲ | paulsmith 3 days ago | parent [-] | | One thing I just recalled is that if you maintain a small exceptions lookup table (i.e. the ones that span state boundaries), you can use ZIP Codes as a way to uniquely look up a county name. | | |
| ▲ | graywh 3 days ago | parent | next [-] | | ZIP codes also span county boundaries that aren't state boundaries -- I know of several in my county alone | |
| ▲ | mulmen 3 days ago | parent | prev [-] | | Why would you do this? | | |
| ▲ | paulsmith 3 days ago | parent [-] | | For example, health care plans in the US are county-specific with regard to premiums, co-pays, etc. (based on demographics). Allowing someone to type in their ZIP Code to get started can be a better user experience than having them pick their county. https://www.healthcare.gov/see-plans/ | | |
| ▲ | mulmen 3 days ago | parent [-] | | Except when it isn’t. I’d be curious to know the population in areas where a zip code spans multiple counties. | | |
| ▲ | paulsmith 3 days ago | parent [-] | | In that case, each county that corresponds to that ZIP Code is shown and the user can disambiguate manually. | | |
| ▲ | mulmen 3 days ago | parent [-] | | Yeah it makes it easier. And I’m appreciative of the idea of making address entry easier for users but if they have to disambiguate did you actually make it easier? I think Zillow does it best. You just type your address in a box and it looks up the normalized full address. That makes everyone happy. |
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| ▲ | chromatin 3 days ago | parent | prev | next [-] |
| My ZIP code happens to be shared by two separate cities and there are a few websites (Github, I'm looking at you) that will fail the payment, registration, etc. attempt if you don't enter the municipality that it THINKS is correct. |
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| ▲ | ProllyInfamous 3 days ago | parent | next [-] | | Exact opposite problem at my former rental: Two different properties with different ZIP codes... but they had the same address on the same road, just a mile apart (different jurisdictions). I lived in a house; the other location was a nail spa. Strangers sometimes visited thinking they were at the right address (they weren't) to get their nails'did (they didn't). | | |
| ▲ | dhosek 3 days ago | parent | next [-] | | A lot of this is on the people doing the platting in the first place. I would note, for example, that where I live in Oak Park, when they replatted the suburb after splitting from Austin Township with a different grid than is used in Chicago and the neighboring suburbs that 1. They kept the Chicago grid on the edge streets of the village so that, e.g., 110 North Austin would be across the street from 111 North Austin and 2. If they had kept the usual new 100 at each block system, the north-south streets on the south end would have been 1200–1249 which would have been identical to the numbers of the next block south in Berwyn and Cicero so the last block on the north-south streets is instead 1150–1199. Contrast the borders of Los Angeles which in some areas are almost fractal in their complexity (there are buildings which straddle the boundary between L.A. and its neighbors and many blocks where adjacent buildings are in different cities). For whatever reason, the powers that be decided that the incompatible address numbering between adjacent cities should be retained so you will have weird discontinuities in building numbering along a block depending on what city the building lies in. I remember my wife having a doctor’s appointment in a building which was one of those which crossed the border so it had two different addresses assigned to it, one for Los Angeles and one for Beverly Hills. | |
| ▲ | dylan604 3 days ago | parent | prev [-] | | > to get their nails'did (they didn't) I'm thinking an opportunity was missed here. |
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| ▲ | dfxm12 3 days ago | parent | prev [-] | | Would ZIP+4 help here? | | |
| ▲ | stackskipton 3 days ago | parent [-] | | Yep, Zip + 4 is pretty pinpoint, generally it's no more than 20 residences and there is plenty of Zip + 4 that is single address. | | |
| ▲ | dhosek 3 days ago | parent [-] | | A lot of P. O. Boxes have their own zip+4 address. You can spot these because the P.O. Box number and the +4 are usually the same (or occasionally the P.O. Box number is the last two digits of the five-digit zip code combined with the +4 so that a piece of mail with a box number and no zip code can be delivered to the correct post office in a large city). | | |
| ▲ | stackskipton 3 days ago | parent [-] | | Yea, PO Boxes generally have their own Zip Code so they use +4 for that. However, if you look at zip+4 for dwellings, it’s still few. My cul de sac with 5 houses has zip + 4 different from house on connecting street. | | |
| ▲ | dhosek 2 days ago | parent [-] | | It’s based at least in part on delivery routes. There’s a less-known 11-digit zip code which is unique for every delivery point (so down to the individual residence). I’m not sure if multiple apartments in the same building have distinct 11-digit zip codes, but this does imply that a zip+4 cannot have more than 100 delivery points within its bounds. | | |
| ▲ | stackskipton a day ago | parent [-] | | Apartments will commonly have multiple Zip + 4 for the building so I imagine each apartment gets unique Zip 11. Open Google Maps, go to Central Park in NYC, search for apartments and randomly pick one. Then go USPS Zip Code lookup (https://tools.usps.com/zip-code-lookup.htm) and punch in the address leaving off any apartment number so it will show all available addresses. I used 225 E 63rd St New York, NY. Appears they have 8 Zip + 4 assigned to the complex. I tried again with building in Philly and same story. Each floor of 16 apartments got its own Zip + 4. |
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| ▲ | drecoe 3 days ago | parent | prev | next [-] |
| ZCTA[0] can (roughly) be used for this purpose https://www.census.gov/programs-surveys/geography/guidance/g... |
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| ▲ | voxadam 3 days ago | parent | prev | next [-] |
| Related: Stop Using Zip Codes for Geospatial Analysis (2019) - 184 points, 131 comments - https://news.ycombinator.com/item?id=42974728 |
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| ▲ | PLenz 3 days ago | parent | prev | next [-] |
| Sometimes they're entire non geographic entities like the IRS |
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| ▲ | mulmen 3 days ago | parent [-] | | Or moving areas like aircraft carriers. | | |
| ▲ | PLenz 3 days ago | parent [-] | | The military postal code system is seperate from the US post office's zip code system. Often (and easily!) conflated but actually operating in parallel. Made even more confusing because many U.S. based entities can be reached in both systems. | | |
| ▲ | mulmen 3 days ago | parent [-] | | Neat! The military postal codes look like ZIP9s, is that a coincidence or is that just the interface with the USPS? |
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| ▲ | Bender 3 days ago | parent | prev [-] |
| zip codes are not geographic areas, they are a collection of mail delivery points. Indeed. My zip is from a neighboring state but has a -xxxx to route specifically to my mail distribution center. Even without the last 4 digits they manage to figure it out, just slower. |
