Osm2pgsql - Lines instead of polygons that represent buildings

Question

So I am using a PostgreSQL database with the PostGIS extension to extract building data with addresses from osm data.

I just discovered that in my dataset, imported with osm2pgsql of the german city hamburg there are some entries in planet_osm_line which have addresses. Those entries are also valid polygons, i tried to transform those LINESTRINGs with ST_MakePolygon and that worked for every entry.

Here is an example of what I am talking about:

So I wondered why osm2pgsql did not interpret them as polygons. To my understanding a valid polygon (closed way) needs identical start and end nodes, which is so far true for every entry.

I might be missing something here, so can anyone with more experience can explain this to me?

Here is the text representation of the geometry from above:

Answer 1

welcome to StackExchange GIS!

It looks like the difference is the tagging of the buildings. Way 171640616 is building:demolished=yes whereas way 171640812 is just building=yes.

If you look at the default style for osm2pgsql, the default settings for building as a tag are to create a polygon (see the OSM Wiki for further details on how this works), but in the first case this tag does not exist, so the addr:housenumber entry is dominant, which is set to linear, which explains the geometry you are getting.