Another thing to note. In the US, Zip Codes do change. In fact, due to closing post offices, the data is more volatile than it has been in a long time.
David. On Fri, Apr 2, 2010 at 9:13 AM, Paul Houle <p...@ontology2.com> wrote: > Anthony wrote: >> >> The actual areas are basically only useful for reverse geocoding >> (click a spot on the map and get the postal code). But whether or not >> that's even possible is highly dependent on whether or not the post >> office provides such information. For some post offices, such >> information is not meaningful. What is the postal code for the middle >> of a highway? Maybe there is one defined, which represents what the >> postal code would be if there were a post box there. But maybe there >> isn't. It depends on the post office. >> > In the US, ZIP codes are really sets of points (addresses that get > delivered to), not geographies. > > There are commercially available ZIP code boundaries that are made > by a process of assigning plausible shapes that fit the points known to > be in the ZIP codes. I suppose these are done with alpha shapes or > maximum-margin or some similar algorithm. > > There's a lot of demand for ZIP code-indexed data in the US because > everybody is familiar with them, and because they're roughly on the > scale of marketing activities: you're likely to drive to stores that > are in your ZIP code or nearby ZIP code. On the other hand, the more I > learn about ZIP codes the more I learn how bad they are: for instance, > ZIP codes are insufficient to determine a person's congressional > district, commonly cross counties, and I'm aware of at least one ZIP > code that spans two US states. ZIPs are also too big to do effective > geodemographics: for instance, the ZIP code 14850 (most of "Ithaca, > NY") contains some very rich neighborhoods, some very white > neighborhoods, and also some neighborhoods that are poor and minority. > There are good commercial databases, however, that give geodemographic > profiles at the census block or individual household level: enough that > you could find out that the most of the 'rich' people in 14850 are > college professors who don't spend ostentatiously so they wouldn't > support a Nordstrom's or a Jaguar dealership. > > Personally I like the TIGER county shapes for spatial control in the > US. These are accurate and tile nicely and, I find I that the union of > several counties is generally a good proxy for the kind of 'semantic > regions' that I work with... For instance, even if I'm targeting a > city, the noosphere density falls off so much in the suburbs that the > county is an effective boundary: and if something out in the 'burbs has > that much 'interestingness' it's probably semantically associated with > the city anyway. > > I'm currently establishing a spatial control system for the world > and it's probably going to be based on second-level administrative > divisions, though I've got good third-levels for a lot of interesting > places. > > > > > > _______________________________________________ > talk mailing list > talk@openstreetmap.org > http://lists.openstreetmap.org/listinfo/talk > _______________________________________________ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk
