Tom Chance [mailto:t...@acrewoods.net] wrote: >Sent: 07 April 2010 11:41 AM >To: Andy Robinson (blackadder-lists) >Cc: Ed Loach; Steve Doerr; talk-gb@openstreetmap.org >Subject: Re: [Talk-GB] West Mids Ward Boundaries > >On 7 April 2010 11:29, Andy Robinson (blackadder-lists) ><ajrli...@googlemail.com> wrote: > > > Its also worth noting how the OS maintains this boundary-line data. >Its not > apparently, as you might have thought, tied to OS MasterMap, which >you would > think would provide precise positioning based upon land ownership >etc. > Instead it's based off the 1:10k mapping, basically StreetView though >not > necessarily that style. So importing boundaries isn't necessarily a >good > idea and in any case is likely to conflict to some degree with >existing > data. That's why prefer a manual process. There are not that many >boundaries > to sort, so it's not like it would take years to do anyway. > > > The NaPTAN import has proved to me that we should never trust >imported data > without our own verification. > > > >That's interesting, thanks. But how do we verify ward boundaries if not >from the open OS data? > >The only other place you can go is your local authority, whose records are >polluted by non-free OS data. That or you extrapolate boundaries from the >electoral register, which lists every street in wards and (one further >level down) polling districts. That would require both the register in an >appropriate format (as a local party officer I have one for Southwark) and >the technical skills & time to do that (which I lack).
I think maybe your second para actually answers the question. Wards are all about people and places, so on the whole one would expect that if a street is in a particular ward then the boundary would encompass at least all of the street, ie the boundary would not run down the middle of the back gardens. Just like with public footpaths it's the text description of the boundary (or what is within it) that appears to be more revealing than the line on the map alone. What I'm meaning by verification is interrogating the boundary line with the features already mapped on the ground. In many cases we know where the back of gardens are for instance, or the position of a water course, railway line or a parish boundary. Many other boundaries, including Ward boundaries, tie in with these features. So, for example, if a boundary actually follows a stream and the stream is in OSM, then logically our boundary should follow the stream, even if the OS have a slightly different alignment for the feature. > >I can't see any better option at the moment than an import from the open OS >data, whether StreetView or the future release of the vector stuff. The Boundary-line data set is vector, so I assume it will be the same product if its also released with VectorMap District. Not withstanding any changes of Boundary-Line in the proposed May update by the OS. Cheers Andy > >Best wishes, >Tom > > >-- >http://tom.acrewoods.net http://twitter.com/tom_chance > > >No virus found in this incoming message. >Checked by AVG - www.avg.com >Version: 9.0.791 / Virus Database: 271.1.1/2795 - Release Date: 04/06/10 >19:32:00 > _______________________________________________ Talk-GB mailing list Talk-GB@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-gb
