[OSM-talk] All you've ever wanted to know about the french cadastre

[Martin Koppenhoefer]

2012/9/27 Vincent Pottier <vpottier at gmail.com>:
> Le 27/09/2012 02:22, Martin Koppenhoefer a écrit :
>> actually it is not only the diagonal line (which is an obvious error),
>> but it is also all or most of the divisions, which don't seem to
>> corrispond at all to real buildings or parts of them (maybe they are
>> property divisions, but then the property in this ensemble is divided
>> quite weird) when confronted with the aerial imagery.
> Looking at the tags on the polygons, you will find that some of them have a
> wall=no
> that canot be seen from aerial.


Interesting, I have never heard before of building=yes with wall=no
but I found documentation in the wiki:
http://wiki.openstreetmap.org/wiki/Tag:wall%3Dno
It looks as if there is an overlap with building=roof

Frankly I don't find "building=yes, wall=no" very intuitive, if I get
the wiki right, this is used for a series of distinct features like
balkonies, constructions "without foundations" (what do you mean by
this? temporary buildings? what does qualify for "foundation"?)
storage sheds and "slight constructions" (I also don't understand what
this means. Do you intend "light constructions"?).

I am particularly opposing the idea to use "wall=no" for a feature
that might have walls but not a roof (balconies), and I do also
generally oppose this tag "wall=no" because of the reasons given above
(not intuitive, mixes different classes, sometimes even
contradictory).

To get this right: I am not opposing the division into several
buildings instead of one outline (judging from the bing aerial these
are indeed several buildings), but the divisions between those
buildings should follow reality (which they apparently don't do at all
in the cadastre version). I am aware that this is simply one example,
but the way it looks makes me fear that there are lots of similar
problems. In this particular case it looks as if manual tracing would
be faster than adjusting the vector version.

cheers,
Martin