This also leads to some very interesting issues, as third parties who automatically ingest the data have a habit of just reading the docs and making the wrong assumptions about what it means in reality.
One example I often encounter myself is Google Maps trying to geolocate my address (city, street name, house number), and then reverse-geolocate that into my postcode. Which sounds like it would work - until you realize that the postcode polygons can overlap. I live in a building where (roughly) each floor has its own postcode, so whenever I try to fill in my address on a website which uses Google's API, it'll "helpfully" auto-fill or "correct" my postcode from 1234AB to 1234AZ. It'll essentially pick a random postcode, because all of them share the same coordinates!
That's Really Really Bad, because the postcode plus house number combination is supposed to uniquely identify a mailbox: it's only a matter of luck that the house numbers aren't reused in the set of postcodes used for my building. They could've just as well reused the numbers at the individual building entrances...
One example I often encounter myself is Google Maps trying to geolocate my address (city, street name, house number), and then reverse-geolocate that into my postcode. Which sounds like it would work - until you realize that the postcode polygons can overlap. I live in a building where (roughly) each floor has its own postcode, so whenever I try to fill in my address on a website which uses Google's API, it'll "helpfully" auto-fill or "correct" my postcode from 1234AB to 1234AZ. It'll essentially pick a random postcode, because all of them share the same coordinates!
That's Really Really Bad, because the postcode plus house number combination is supposed to uniquely identify a mailbox: it's only a matter of luck that the house numbers aren't reused in the set of postcodes used for my building. They could've just as well reused the numbers at the individual building entrances...