How are building outlines extracted and how often are they updated?

Hi all

We are developing an online crowd-sourcing platform for Athens, Greece, where users will be able to add data for each building in the city, such as height, age, construction type etc.

OSM building polygons currently exist and are up-to-date for most of the city of Athens. However, there are parts of the city where there is a lack of building
outline data.

Do you know how these data are extracted? Is it from satellite images?

Do you also know how often are these data updated? We wouldn’t mind developing our platform using the building polygons that are currently available, but we need to know that there is a high chance that these data will be updated in the near future. Otherwise, we need to find other sources for the building polygons.

Thanks a lot!

I’m not sure I’m understanding your question, but it seems to me that you don’t have clear ideas about how OpenStreetMap (OSM) works; you can start having a look here:

OSM mappers can directly map things they see while walking or cycling around, also using registered GPX tracks or notes.
More frequently, they can map things from their computer using, as a reference, aerial or satellite images for which it is possible to derive geospatial information:
To clarify: mappers uses OSM editors (the in-brower iD editor, or JOSM, or others …) to draw the outline of buildings (and roads, and many other things…) they see on the images, and adding also many additional information
The best thing is that you directly improve the OSM database adding height, age, construction type information in OpenStreetMap using the appropriate tags. See here for more detailed info on tags for buildings in OSM:
Data are updated if people update them :slight_smile:

Please be aware and remember that if you use OSM data together with other information and you release a derived/integrated product, you have to release all the data as open data under the ODbL licence. See the copyright page for OSM here:


There are many sources of building footprints and they depend on the area:

  • manually drawn from satellite imagery shared with us by Bing, Maxar, Esri, Mapox or aerial imagery from local governments
  • imported from local government data
  • imported from what Microsoft generated with machine learning

People usually update areas as they want and as they notice any new buildings.
There’s no coordinated update plan as such on a global scale (in some less developed countries the Humanitarian OSM Team created projects to map buildings)