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.
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?