[Talk-GB] Places and postcodes -- nodes/areas?

[Matt Williams]

On 10 September 2012 23:07, David Fisher <djfisher81 at gmail.com> wrote:
> My other (related) question is to do with postcodes. Some postboxes nearby
> have been tagged not only with "ref=xxx" (containing the first part of the
> postcode plus a reference no.) but also "postal_code=xxx" (again containing
> the first part of the postcode), meaning that, again, a lot of streets &
> POIs become identified by Nominatim with this postcode (e.g.
> http://www.openstreetmap.org/browse/node/363996567).  Should *all* postboxes
> be tagged with "postal_code" in this way?  What about streets themselves?
> For streets, does the (first part of the) postcode need to be displayed on
> the street sign for this to be done?

The 'ref' part will be directly from the postbox label itself. I'd
imagine that the majority of the postal_code entries are from
http://dracos.co.uk/made/locating-postboxes/. Unless we have another
source of postcode data I'm not aware of? Even with the Dracos stuff,
I'm unsure of the licensing details.

I would be surprised if post boxes being labelled with postal codes
were affecting which suburb a certain street is associated with in
Nominatim. Postcodes and localities are almost unrelated as the Royal
Mail have their own way of doing things. The real point is that post
codes aren't areas, they're merely a set of addresses. They can
sometimes be thought of as areas but it's not how they're defined and
treating them as such can cause errors like you mention.

About postcodes on streets: it should not really be done. Streets do
not have postcodes, only the houses on them. For example, it's quite
common to have a street with different postcodes on either side of the
road and certainly common to have multiple postcodes along their
length. For postcode tagging, I wrote up a little about how I do it at
http://milliams.dev.openstreetmap.org/postcodefinder/tagging/ so I'd
recommend doing that (or if you want to avoid relations, at least
adding addr:street to the houses).

-- 
Matt Williams
http://milliams.com