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Shmias's Diary

Redundancy in Buildings

Posted by Shmias on 20 September 2014 in English.

I’ve noted that most of the complex and important buildings in Berlin are duplicated for each geometry type. For instance the Berlin TV Tower:

Berliner Fernsehturm

As you see here its a tower with a fancy building on its base. This is what it looks like in Openstreetmap:

Fernsehturm Karte

So I suppose in osm this object should be a relation with different building parts as ways.

That is so, but certain tags a duplicated through this structure.

The same applies on the nearby Saint Mary’s Church relation/node,the Bodemuseum relation/way/node and several other buildings.

What do you think is the reason for that? Well, my theory is that many services can’t really handle relations. Such as wheelmap and the main renderer.

Mapnik won’t show any label because of a relation tagged with name. At least not for museum& place_of_worship so a visitor will assume that the name is missing and add it to the structures he can see clearly on the map. Or he’ll do it intentionally for the renderer.

Should I post this as an issue?

Location: Mitte, Berlin, Germany
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Discussion

Comment from mapper999 on 20 September 2014 at 16:37

Hi,

I just had a look at the Berlin Fernsehturm and found several issues which might cause the missing label and the broken rendering:

  • The Fernsehturm consists of many different overlapping building=yes ways which should actually be building:part=yes. This is probably a leftover from early 3D-mapping when the building:part key was not yet used.
  • The main tags are on a building-relation which is not yet an approved nor widely used feature. It is also not supported on simple editors like iD etc. Instead there should be an area (or multipolygon) for the whole building complex with the main tags.
  • The Fernsehturm is many features in one: tourism=attraction, tourism=viewpoint, man_made=communication_tower. Not all of these tags are compatible with each other. Maybe the whole building complex should get the tourism=attraction, while the tower part gets the tourism=viewpoint and man_made=communication_tower. I think all the other man_made=tower tags should be deleted.
  • There have been a lot of 3d experiments going on for the tower with different tagging schemes.
  • There is a broken multipolygon with overlapping and touching inner rings for the pedestrian area around it, which probably causes the rendering issues.
  • There are some entrance and housenumber nodes near the building, where it is not really clear where they belong to.

The Berliner Fernsehturm is a very famous building in Germany, so a lot of mappers probably tried to “improve” it and added more and more tags and details.

I think the whole building complex needs a cleanup by an experienced mapper (with 3d tagging experience) who knows the area/building. The same probably applies to the other buildings you mentioned.

I don’t think posting an issue for the renderer helps here. The building relation has been proposed 7 years ago and is still not approved nor is it really clear from the proposal how it should be used. The problem with the pedestrian area overlapping parts of the building is due to a broken multipolygon which is a tagging issue and not a renderer issue.

Comment from Pieren on 22 September 2014 at 14:31

I think too the relation type=building is the problem. If the block is a single building, then create a multipolygon relation. If it is different buildings, then create a surrounding polygon for the tower (or keep the tower tags only on the tower polygon)

Comment from robert on 22 September 2014 at 21:46

Ah germans.

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