ELI5: how are type=building relations used?

[ivanbranco]

Hi,

could someone explain to me what's the usage of type=building relations? When the renderer sees a type=building tag, what changes in its rendering?

[StrandedKitty]

Hi. If a type=building relation has a member with role outline (either way or relation) than this member doesn't get rendered.

[ivanbranco]

If a building:part is mapped, the outline isn't rendered even without type=building (and a type=building is created only when there's at least one building part). I don't understand the difference.

[StrandedKitty]

A way with building:part=yes exterminates all the building=* ways it intersects (with intersection area greater than some epsilon). type=building relations are meant to make this behaviour more predictable. If you have such a relation you can explicitly specify the outline and the parts and get predictable and very simple behavior: outline is hidden, parts are rendered.

Also, if a building:part is in a type=building relation and has a role part than it won't try to hide buildings intersecting with it. Because it is implied that the outline is hidden anyway, so there's no need for this.

[ivanbranco]

Ok, so it makes sense to suggest it mainly for "hanging" parts as the Wiki does, since they could intersect outlines of other buildings.

What happens tho if the "outline" member is tagged as building:part=*?

[StrandedKitty]

What happens tho if the "outline" member is tagged as building:part=*?

It gets hidden anyway because it's the outline.