[OSM-talk] Duplicate Buildings

[john whelan]

Many thanks for putting some numbers on this.

Warin's comment would suggest it may also be more than just buildings that
are involved.

For buildings the total number as a percentage is small unfortunately they
tend to cluster so are more of a problem than if they were more spread out.

John

On Sat, Mar 11, 2023, 07:40 Frederik Ramm <frederik at remote.org> wrote:

> Hi,
>
> I think an automatic fix of the problem is possible, however it would be
> a good idea to try and find out what the root cause of the problem is -
> bad software, bad imports, bad instructions?
>
> To get an idea of how big the issue is, I did this on a standard
> rendering database:
>
> create table buildings as (select way,osm_id from planet_osm_polygon
> where building is not null)
>
> select a.osm_id, b.osm_id into duplicates from buildings a, buildings b
> where a.osm_id < b.osm_id and a.way ~= b.way and st_equals(a.way,b.way);
>
> This took a few days - probably it could have been done more efficiently
> - and resulted in a list of about 70k buldings world-wide that are exact
> duplicates (geoetry-wise) of other buildings. The list is here:
>
> http://www.remote.org/frederik/tmp/duplicatebuildings.csv
>
> Some buildings are in OSM three or four times (contained i nthe above in
> the form of "a is duplicate of b, b is duplicate of c") but I've
> extracted them in extra files:
> http://www.remote.org/frederik/tmp/triplcatebuildings.csv and
> http://www.remote.org/frederik/tmp/quadruplicatebuildings.csv)
>
> I don't have the time to analyse the situation in more detail at present
> so if anyone wants to take the above lists as a basis for deeper
> analysis...
>
> Cheers
> Frederik
>
> --
> Frederik Ramm  ##  eMail frederik at remote.org  ##  N49°00'09" E008°23'33"
>
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