Just a note to make sure we are all comparing apples with apples, but US (and Australian) postcodes are much less specific than Canadian (and UK) postcodes.
AFAIK In Canada and the UK a postcode gives you an exact address, or pretty close to (around 10-20 properties to each postcode?). In the USA and Australia, a post code just gives you a 'suburb' (hundreds to thousands of properties to each postcode).
Some postal codes contain at least 5000 people, but at the same time my apartment building has one of its own.
I think it's largely based on how mail is distributed, as they are Canada Post identifiers. My 5000 person hometown has no delivery -- everyone goes to the one post office. But my apartment building has its own little postal box thing, which requires a key from the mailman, which is a special case compared to dropping in mailboxes on the rest of the street.
I don't suppose there's any postal workers on here to chime in?
Generally speaking, a postcode refers to a road, part of a road (if the road is very long), or a single organisation. Roughly, you will have 1-100 properties per postcode.
The first line of the address (often just the house number) and the postcode are sufficient to yield the entire address.
> expressly forbidden to [...] use in any database and/or application for the purposes of providing, updating or maintaining any publicly available postcode look up or finder functionality;
You're not allowed to use the Australian post code database as provided by Australia Post to provide a lookup or finder functionality that's publicly available.
That is strictly true, but I've possibly found a way around this and have posted a CC licensed version (the most open I was able to find) on GitHub accordingly. https://github.com/joahua/AusPostcode
I see these are built on the Australian Bureau of Statistics "approximate" postcodes which are matched to census districts and therefore more useful for demographic analysis; no CDs cross postcodes in this dataset. There are a bunch of similar geographic datasets available from the ABS, including electoral boundaries, local government areas and so on: http://www.abs.gov.au/websitedbs/D3110124.NSF/24e5997b9bf2ef...
All of that data is approximated by the ABS from whatever body controls the "real" versions, but is 99% good enough for anything you'd want to do with it.
Australia Post, on the other hand, don't really use postcodes to deliver mail anyway, I've been told. They're a vestigal construct which are very prominent in people's minds but so fraught in the implementation that any systems which analyse them (including Australia Post's) work against them rather than with them. I didn't know about Canada's system — that sounds like a much better idea!
Actually, there are a few. For example, QLD 4352. It's just a collective postcode that covers everything around Toowoomba that hasn't been given a postcode. Using the suburb name instead of 4352 is a whole lot more productive.
It's eight non-contiguous areas as far north as Caboolture and as far south as Casino, the biggest of which are not much larger than Brisbane City Council.
Edit:
There's a treasure trove in the post code boundaries of utterly bizarre things that only past houses being in weird places can at times explain.
Furthemore, Russian govt releases full information on Postal Codes, Cities, Streets and even House numbers on those streets. For free, but in very large files http://fias.nalog.ru/Public/DownloadPage.aspx
Do you know how accurate that is? Every time I've seen census zip code data it comes with a big disclaimer that its only accurate as of the last census. The USPS changes zip codes at will.
TIGER is the Census geo data set. This is "zip code tabulation areas," not strict zip codes. The Census does update its maps more frequently than every 10 years though.
They are not very accurate if you are trying to map addresses to zip codes, for example. The data is compiled based on Census tracts. For each census tract, it tells you the most common zip code in that tract.
http://www.census.gov/tiger/tms/gazetteer/zips.txt