Hi, I think we should perhaps add a new section in the cadastre documentation: the purpose of the cadastre, and the way it is made.
In France you need to ask for a permission from the public authority (the municipalities) before to make a new building. It include a detailed map of what you want to do. This is the map added to the cadastre (at least the local copy), each time an authorisation is asked. So the data in the cadastre is an aggregation of every building map provided by the "architects" (not always the case). But you are also authorized to build some new extension of a house without to ask permission, if the new build is under a predefined size or kind of building. So, many people are adding new portion of building just at the limit size, that's why we can sometime see small part of building on the cadastre. It can be not visible from the street or aerial imagery, but it is still the reality of the building ! All the wall=no polygon are build on the same kind of rules: you need to ask for an authorization if you build a "full" house with foundation, but you can do almost what you want if the building as no foundation, especially in the case of agricultural buildings (which seem to be the case of our current example). So if you build something without real wall, or without a roof, it's identified in a different way on the cadastre map. Sylvain 2012/9/27 Lester Caine <les...@lsces.co.uk> > Pieren wrote: > >> On Thu, Sep 27, 2012 at 12:01 PM, Martin Koppenhoefer >> <dieterdre...@gmail.com> wrote: >> >>> >buildings should follow reality (which they apparently don't do at all >>> >in the cadastre version). >>> >> How can you say that from an aerial imagery ? It is also possible that >> the cadastre is outdated. Like any source of contribution, including >> local survey. >> > > Pieren > Many of the buildings moving away from the one identified simply do not > even fit the footprint on the bing imagery and many of the 'divisions' seem > to follow the ridge of a building rather than a difference between roof > colour. The current blocks simply make no sense! It is not possible from > the aerial imagery to identify divisions so unless those divisions are > identified by other means ... such as a clear identification in Cadastra > ... or better still by local knowledge ... then the building should simply > be an outline! Now that I have scanned some of the French material I must > say that it is of very low quality and all of the stuff I have reviewed > needs at least SOME work to bring it up to a better standard. At best all > one can say currently is 'there are some buildings round about here' ... > and stripping unsubstantiated detail would at least be a start. > > -- > Lester Caine - G8HFL > ----------------------------- > Contact - > http://lsces.co.uk/wiki/?page=**contact<http://lsces.co.uk/wiki/?page=contact> > L.S.Caine Electronic Services - http://lsces.co.uk > EnquirySolve - http://enquirysolve.com/ > Model Engineers Digital Workshop - http://medw.co.uk > Rainbow Digital Media - > http://rainbowdigitalmedia.co.**uk<http://rainbowdigitalmedia.co.uk> > > > ______________________________**_________________ > talk mailing list > talk@openstreetmap.org > http://lists.openstreetmap.**org/listinfo/talk<http://lists.openstreetmap.org/listinfo/talk> >
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