[OSM-talk] Duplicate Buildings

[Frederik Ramm]

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"