With regard to "street_polygons", what does "mapped as polygons" mean?

[SomeoneElseOSM]

https://shortbread-tiles.org/schema/1.0/#layer-street_polygons says:

Layer “street_polygons”
Holds polygons geometries of certain streets mapped as polygons

OSM doesn't have an explicit area type, so there are a couple of ways that things can be thought of as polygons:

1. It's a closed way, and all objects with particular tag/value combinations can be thought of as areas
2. It's got an explicit area=yes tag

The highway tag isn't explicitly an area tag - a residential road that forms a circle is just a circular road, not a large area. However, a highway=pedestrian arguably is. Some mappers use area=yes on these but some do not, meaning that some pedestrian areas aren't detected as such - see https://pnorman.github.io/tilekiln-shortbread-demo/#18/53.959634/-1.081985 and https://pnorman.github.io/tilekiln-shortbread-demo/#18/53.960158/-1.084093 .

After a quick look, I'm unaware of any mapping of genuinely circular (i.e. not area) highway=pedestrian ways, so it would make sense to me to say "if a highway=pedestrian is a closed way, assume it is an area". That code change would need to be implemented by whoever implements Shortbread-schema tiles, of course. That's what I've done when I've consumed OSM data elsewhere.

However, separately to that, it'd be good if the documentation here could clarify that either "mapped as polygons" means "a highway with an area=yes tag, or that certain sorts of closed way highway values such as pedestrian are assumed to be areas.

[pnorman]

I would only consider it an area if it has an explicit area=yes tag or we were adding it based on a area:aeroway key.

If we set a rule that highway=pedestrian without area=yes made it into this layer and applied the same logic to the streets layer then extending a way could make it disappear from that layer.

[SomeoneElseOSM]

For highway=pedestrian, the query for problem ways is something like https://overpass-turbo.eu/s/2hto (nwr["highway"="pedestrian"][!"area"]({{bbox}})(if: is_closed() == 1 );).

As an example compare OSM Carto https://www.openstreetmap.org/way/16299012#map=19/51.483151/-0.309036 with Shortbread https://www.openstreetmap.org/way/16299012#map=19/51.483151/-0.309036&layers=S (and also FWIW iD).

https://wiki.openstreetmap.org/wiki/Tag:highway%3Dpedestrian says to add area=yes to areas, which is good advice and lots of people do, but quite a lot of people don't.

I went through lots of these in UK and IE when deciding whether to process them as areas or not, and the vast majority there were areas. Can you think of anywhere where I could run that query where the majority of ways would be actually closed linear ways rather than area ones?

Because of that I'd suggest treating ["highway"="pedestrian"][!"area"](if: is_closed() == 1 ); as areas.