How to get a set of all buildings of an OpenStreetMap section in form of single points / Multiple polygons as one point

Question

The objective is to get a set of all buildings of an OpenStreetMap section in form of single points in a shapefile.

1. I downloaded the section from OSM.
2. Imported the section into QGIS (and later imported it into a PostGIS db using osm2pgsql)
3. To transform the polygons (representing buildings) into points I used the Polygon Centroids function

Unfortunately some of the buildings are represented by multiple polygons subsequently I did get multiple points for one building which I is not what I wanted.

Searching the web I found out that these polygons should be multipolygons but neither QGIS nor osm2pgsql does import these relations so that I could merge the polygons of a building

Any ideas how I could get single point list of the buildings?

Answer 1

You can create a very small buffer around your polygons and dissolve all, before creating the centroids.

This would also unite buildings that share a common wall.

Answer 2

Used the OSM Download Plugin

Used your coordinates

downloaded the .osm

Loaded this in to QGIS

Extracted 'Building = Yes'

Used the Vector > Geometry Tools > Polygon Centroids

You can delete unwanted centroids or clean up the data before creating the centroids all data has attribution.