[OSM-dev] Programatic reconstruction of postal code areas

Jo winfixit at gmail.com
Wed Mar 29 08:41:36 UTC 2017

What I did, at some point when I was trying to figure out zones of bus
stops, was to create a MapCSS style which gave me different background
colours for each numbered zone. This helped me to visually find the
'outliers', based on the ones that I did already figured out the zone for.

For postal_code boundaries, they will very often follow existing
boundaries, except where they don't... so I would say it is possible to
draw them by mostly following the existing admin_boundaries. If we ever
want to draw parishes, we'll probably have to 'wing it' in a comparable
way. To me this feels like how we started drawing everything all the way
back when OpenStreetMap was a blank canvas. We start with something, if
it's wrong we correct it and slowly but surely we get to a point where we
have the best data. And possibly OSM becomes the only place where those
shapes can be found. It's unlikely they are exactly what the post offices
use, but it's even more unlikely that the post offices will ever share them
in a way we can use them. And if all the houses with that post code are
within them, they are 'good enough'.

Saying that you should contribute them to Nominatim might be 'the right
thing to do', but then we lose the possibility to improve them
incrementally, which is exactly what OpenStreetMap excels in.


2017-03-29 10:20 GMT+02:00 Tom Hughes <tom at compton.nu>:

> On 29/03/17 08:58, Frederik Ramm wrote:
> On 29.03.2017 09:10, Alex K wrote:
>>>   * For one, this type of information is already part of
>>>     OSM: http://wiki.openstreetmap.org/wiki/Tag:boundary%3Dpostal_code
>> Generally we don't like data that is impossible (or difficult e.g.
>> "knocking on doors") to verify on the ground, but we do make exceptions
>> for admin boundaries and, usually, postal code boundaries.
> If the postal code boundary is a genuine thing that exists then sure.
> I don't know about the countries in question, but in the countries that I
> do know about there is no such thing as a postal code boundary because the
> authority that assigns postal codes doesn't do so using geographic areas
> like that, and doesn't special any specific boundary.
> Rather they are just defined by a list of addresses, being a set of
> addresses that are a convenient group to deliver to.
> Now obviously you can draw any number of shapes around those addresses but
> none of those shapes is in any way an official or definitive boundary for
> the postal code.
> Tom
> --
> Tom Hughes (tom at compton.nu)
> http://compton.nu/
> _______________________________________________
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> dev at openstreetmap.org
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