[Talk-GB] Quarterly Project: Addresses and Postcodes

Colin Smale colin.smale at xs4all.nl
Thu Oct 19 13:07:10 UTC 2017

Points - as in delivery points (letterboxes). If you try to analyse the
postcodes into areas, you will find all kinds of exclaves and enclaves.
To go from a postcode+house number to lat/long, you need to do a lookup
in the PAF. If you only have a partial code, you can get an
approximation You cannot go from an arbitrary lat/lon to "the postcode",
without first mapping the location to a "building" that has one or more

I am 99% sure that CodePoint Polygon is not normative - it is just a
bunch of Voronoi polygons arranged around the points. If a new delivery
point is created (a new building for example) it will not tell you
(definitively) what the postcode will be. Many non-residential
buildings, particularly in rural areas (farm outbuildings for example),
are not "addressable" with a postcode/number (or name). Just because
they happen to fall into a certain polygon, it does not imply that the
postcode (if one were ever needed) would be X. 

The value that Royal Mail recognise in the PAF is the ability to go from
a postcode to a location for the purposes of delivery planning - both
their own, and of third parties, plus that it can form the basis of a
complete list of all "addressable" units in the country. 

I am pretty sure as well that route planners work by first translating
the postcode to lat/lon, then routing to the nearest point to there -
i.e. they don't actually have the postcode for every individual
household/company etc. 

Deriving your own polygons from the points has been tried before: 




On 2017-10-19 14:00, Steven Horner wrote:

>> Postcodes refer to points, not to polygons.
> Are you saying a point in OpenStreetMap terms?
> UK postcodes generally cover an area/polygon. How big that area is appears to come down to how much mail that area is likely to receive, I think that's how its described on Wikipedia. So it could cover one building, a street or a huge area if rural.
> Ordnance Survey sell CodePoint Polygons which is the polygons each postcode covers. Obviously we can't use that. 
> On Thu, Oct 19, 2017 at 12:31 PM, Colin Smale <colin.smale at xs4all.nl> wrote:
> In the UK, this algorithm is useless if you expect to get the actual address that you could send a letter to, or that you could ask for directions to.
> On 2017-10-19 13:23, Marc Gemis wrote: 
> Maybe it is interesting to repeat how Nominatim resolves addresses,
> just in case someone wants to do a search after adding an address.
> - Nominatim starts from an address point (or building way with
> address). It takes the house number from it and the street name.
> - It tries to match the street name with a nearby street.
> - The rest of the info, suburb, city, country, etc are taken from the
> way. i.e. it looks in which boundary the way lies and work its way up
> the admin levels.
> - In case there is no boundary, it can use a place node as well to
> determine the name of a certain admin level, but that is less precise
> - postal codes are taken from the address point, when specified. This
> is needed in UK/USA but not in e.g. Belgium or Germany.
> http://nominatim.openstreetmap.org [1] is your friend to understand where
> the data is coming from.
> Of course, if you only work with a relational database (as Lester
> pointed out), one prefers all data on the address node.
> Relational DB with GIS extensions do not need this (e.g. Nominatim).
> Nominatim's approach currently has problems with streets on the border
> of e.g. 2 villages. Sara Hoffmann (Lonvia) told me that there are some
> plans to fix this.
> regards
> m.
> On Thu, Oct 19, 2017 at 10:35 AM, Adam Snape <adam.c.snape at gmail.com> wrote: I'm convinced that many such addresses are unnecessarily long (are there
> really multiple Weldons in the Swanscome postal area?). Nevertheless we
> should have a way of mapping them if they are the official address. I agree
> that more general guidance would aid consistency. My address mapping
> practice is as follows. I would welcome correction if others feel I am doing
> something incorrectly::
> The post town
> https://en.wikipedia.org/wiki/List_of_post_towns_in_the_United_Kingdom [2] is
> tagged as addr:city (whether or not it is a city or indeed whether an
> otherwise more important place is nearer). Though this should all be in
> upper case when used I add the tag in lower case with an initial capital
> letter as it would normally be written in a sentence.
> For sub divisions of this area the wiki has documented tags addr:suburb and
> addr:hamlet. I tend to default to suburb everywhere except when dealing with
> an actual isolated hamlet. Where there are two subdivisions as in Steve's
> example, I'd use hamlet for the smaller one  and suburb for the larger one.
> The wiki suggests to avoid addr:street and addr:place together but I use
> them for things like named retail/business parks where there is also a
> street address eg. https://www.openstreetmap.org/way/527520264 [3]
> I do not tag the name of the property separately if it is the same as the
> main name=* tag
> Counties have not been formally part of postal addresses for many years.
> Royal Mail permits people to optionally add the name of the old Postal
> County, modern administrative or ceremonial county, or traditional county to
> their address according to their personal preference, but this plays no role
> in delivery. So I do not tag a county in the address.
> So I'd tag Steve's example: name=The Spring River, addr:street=Talbot Lane,
> addr:hamlet=Weldon, addr:suburb=Ebbsfleet Valley, addr:city=Swanscombe,
> addr:postcode=DA10 1AZ
> I hope that helps
> Adam
> On 18 Oct 2017 11:49 p.m., "Steve Doerr" <doerr.stephen at gmail.com> wrote:
> On 10/10/2017 19:07, Robert Whittaker (OSM lists) wrote: 
> It doesn't seem to have been mentioned here yet, but this quarter's UK
> mapping project is to improve addresses and postcodes:
> https://osmuk.org/uncategorized/jump-in-to-our-quarterly-mapping-project/ [4]
> It would be useful to have some guidance on tagging for UK addresses. For
> instance, how would you tag the different elements of the following address
> for a pub/carvery that opened recently near me:
> The Spring River
> Talbot Lane
> Weldon
> Ebbsfleet Valley
> DA10 1AZ
> Regards,
> Steve
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[1] http://nominatim.openstreetmap.org
[3] https://www.openstreetmap.org/way/527520264
[5] https://lists.openstreetmap.org/listinfo/talk-gb
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