On 26 February 2013 22:08, Aidan McGinley <aidmcgin+openstreet...@gmail.com> wrote: > is the actual output that would get loaded onto OSM.
Please don't load this data into OpenStreetMap. It's not a good idea. 1) The source data appears to be heavily overprocessed. "Users should note that postcodes that straddle two geographic areas will be assigned to the area where the mean grid reference of all the addresses within the postcode falls." So while you're trying to map postcodes to a particular building in OSM, what's actually happening is that the real postcode locations are first being averaged to a centroid, then that postcode centroid is assigned to a given geography (e.g. a LSOA, or whichever geography you are using), and then you're taking the centroid of the geography (not the centroid of the postcodes) and finding a random building in OSM that overlaps that geography centroid, then adding the postcode to the building. So you're adding postcodes to whatever building just happens to be at the centroid of the geography, when all we know is that the centroid of the postcodes is somewhere within that geography. Having postcode data in OSM is useful, but this appears to be very haphazard. There's no guarantee that the given building is anywhere near the postcode centroid (the postcode centroid could be at the edge of a given geography) and it's no surprise that each geography could have multiple postcode centroids. There are other approaches. We have access to postcode centroids from elsewhere, if we were to pick just one building per postcode to assign a postcode to, it would be better to use the centroid of the postcodes, rather than the centroid of a geography that the centroid of the postcodes happens to fall within. 2) The license is unclear "ONS Intellectual Property in the postcode products is supplied under Open Government Licence terms (see Related Links)." Sure, OGL, great, but... "The ONSPD is a Gridlink® branded product that pulls together data from members of the Gridlink® Consortium (Royal Mail, Ordnance Survey, National Records of Scotland, Land & Property Services (Northern Ireland) and ONS)." So the ONS might be happy to put their own IP (presumably the act of mapping postcode centroids to geographies) under OGL, but as it says above there's a bunch of other IP rights in the database, and the ONS makes no statement on the licensing of the data. 3) We don't want to import this stuff anyway Postcode centroids have been discussed many times before, and the position we've taken is that importing them does not help our mappers. It's derived data, not the kind of thing that we actually map. We use the centroids in various visualisations and QA tools, we can expand them out to voroni polygons to help figure out what the real postcodes might be, but what we're aiming for is for buildings to be assigned the *correct*, actual postcodes. Until we get some real, full detail, all 28m buildings, data (e.g. the PAF) under a suitable license, then please don't import centroids or anything derived from them. Cheers, Andy _______________________________________________ Talk-GB mailing list Talk-GB@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-gb