Underground building parts sprouting like mushrooms at the Paris Opera

[nvkelso]

• What did you see? Lots of random building boxes near Opera metro station in Paris.
• What did you expect to see? Building boxes that are underground should generally be marked as such so the style can hide them. Looks like these are marked indoor=*, so maybe they shouldn't show up in the buildings layer at all?

See also:

• https://tangrams.github.io/bubble-wrap/#19/48.87068/2.33222
• Tunnel paths should receive different treatment tangrams/bubble-wrap#251
• https://www.openstreetmap.org/edit?way=475595515#map=20/48.87056/2.33154
• https://wiki.openstreetmap.org/wiki/Simple_Indoor_Tagging

[zerebubuth]

One way of dealing with this is to parse the level tag (including the M;N syntax - perhaps take the max?) and assign location: underground when level < 0. That would allow existing processing to work on these features.

It's worth noting that the building:parts and highway=footways both have level tags, and looks worth doing the location: underground processing to both so that they can both be hidden. Otherwise, the footpaths look quite confusing and aren't useful for an above-ground traveller at all.

[nvkelso]

location: underground and layer: [-1, -2, -3, -4, -5] (not level) are probably conflated a bit in Mapzen house styles:

• Not rendering road over building correctly tangrams/cinnabar-style#30
• https://github.com/tangrams/bubble-wrap/blob/gh-pages/bubble-wrap-style.yaml#L3611-L3614

Right now we block rendering any underground building, but if we see it's level is negative we don't extrude it. That'll need to be re-evaluated.

(I favor marking any negative layer and any negative level as location: underground).

[matkoniecz]

Note that negative layer tag does not mean that object is underground.

(see http://wiki.openstreetmap.org/wiki/Key:layer - Things to avoid - Using negative values to describe something to be underground. Use location=underground for this purpose.)

[nvkelso]

@matkoniecz Thanks for the tip! There's quite a bit of funky data here so we need to balance preventing egregious rendering errors with showing original data.

[nvkelso]

Still a problem:

[nvkelso]

I think really this is a tagging issue upstream, closing.

[zerebubuth]

Looks like a lot of those underground buildings could have location=underground and we'd handle them better. Alternatively, perhaps we could be more robust to this sort of thing by inferring location=underground from the level tag being negative?

[nvkelso]

See #1304 (comment) – negative levels don't neccesarily mean underground. So instead of being clever suggest the data is cleaned up.

[zerebubuth]

If I may be pedantic for a second; the wiki says that negative levels don't mean underground. However, that might have been the intent of the person who mapped those.

You are right, and we should "fix" the data to make it more consistent in its use of location=underground. If we find that this is a widespread problem outside Place de l'Opéra, then it might imply that, whatever the wiki says, in practice people are using negative levels to indicate underground-ness.

[nvkelso]

There's been enough discussion here to warrant reopening the issue (to be acted on at some later date)...