Feature request: Barriers layer(s)

[westnordost]

Barriers are currently omitted from the shortbread schema. At least point barriers such as bollards or gates are important to see on maps which roads are accessible.

There should probably be two layers:

1. point barriers: gate, bollard, lift_gate, block, cycle_barrier, swing_gate, stile, kissing_gate, turnstile, ...

2. line barriers: fence, wall, hedge, retaining_wall, man_made=embankment but also city_wall and natural=cliff

Regarding conflation, I think it makes sense to lump all those different gates into one (or if necessary have a second property tell them apart).

[pnorman]

How's this for a starting place for lines?

Layer "barrier_lines"

Properties

Field Name	Type	Description
kind	string	see Features section for possible values

Features

kind	OSM tag	Geometry	Zoom
fence	barrier=fence	line	14+
wall	barrier=wall	line	14+
hedge	barrier=hedge	line	14+
retaining_wall	barrier=retaining_wall	line	14+
city_wall	barrier=city_wall or historic=citywalls	line	14+
cliff	natural=cliff	line	12+
ridge	natural=ridge	line	14+
arete	natural=arete	line	14+
embankment	man_made=embankment	line	14+
chain	barrier=chain	line	14+
ditch	barrier=ditch	line	14+
guard_rail	barrier=guard_rail	line	14+
handrail	barrier=handrail	line	14+
jersey_barrier	barrier=jersey_barrier	line	14+

I'm most skeptical about ridge and arete, and I wonder if some of the barriers at the end can be combined.

[joto]

It feels a bit weird to me to declare a cliff or an embankment a "barrier". Sure it can be a barrier in certain situations, but it feels different to me.

We should probably talk about the practicalities of rendering maps here, for instance whether these will all be rendered in the same place in a layer hierarchy. For instance I would expect a cliff to be more like part of the landscape and therefore be rendered below roads, while a chain has to be rendered above roads to make sense.

There is also the question of symbols used and, in particular, directionality of some of these. An embankment has a lower and an upper side, a chain hasn't. Which of these symbols can appear in a simpler map using just a single kind of symbol, say a black line and which very likely need a specialized symbol. We need to think about these things to decide whether it makes sense to group them all as "barriers".

This is the first time I came across the "barrier=ditch" tag which is, I believe, not well thought through, especially considering that its wiki page uses what is clearly trenches as illustration which would not fit the barrier=ditch description.

[westnordost]

I think most maps would probably want to distinguish between

1. a normal barrier (wall, fence, ...)
2. a barrier that is part of the landscape or should be rendered differently (e.g. retaining wall maybe)
3. larger structures, like city walls

[SomeoneElseOSM]

It makes sense to have a linear natural layer and have tree_row, cliff, ridge, valley (and possibly reef and others) in that.

[pnorman]

Taking the above comments into consideration, how does this sound?

Layer "barrier_lines"

Properties

Field Name	Type	Description
kind	string	see Features section for possible values

Features

kind	OSM tag	Geometry	Zoom
fence	barrier=fence	line	14+
wall	barrier=wall	line	14+
hedge	barrier=hedge	line	14+
retaining_wall	barrier=retaining_wall	line	14+
city_wall	barrier=city_wall or historic=citywalls	line	14+
chain	barrier=chain	line	14+
ditch	barrier=ditch	line	14+
guard_rail	barrier=guard_rail	line	14+
handrail	barrier=handrail	line	14+
jersey_barrier	barrier=jersey_barrier	line	14+

barrier=ditch is fairly widely used and rendered in some styles. Reviewing both the British and American dictionary definitions all the example photos on the wiki page are ditches. We should include it.

Adding a linear natural layer is a good idea and tags like cliff, etc would go there

[SomeoneElseOSM]

(just looking at barriers for now) https://taginfo.openstreetmap.org/keys/barrier#values suggests a couple of others with higher usage as ways than jersey_barrier (which is on the list):

kerb						2 434 512	7.87%		445k ways
gate						6 208 697	20.07%		254k ways
bollard						896 780		2.90%		56k ways

I'd exclude this because it is arguably not relevant to general purpose map:

yes 152 189 0.49% 102k ways

and for completeness the other values' usage as ways, which is less than jersey_barrier:

chain						43 880		0.14%		9k ways
block						195 640		0.63%		7k ways
toll_booth					61 388		0.20%		5k ways
lift_gate					550 462		1.78%		2k ways
entrance					99 695		0.32%		1244 ways
stile						100 717		0.33%		716 ways
swing_gate					120 479		0.39%		389 ways
cycle_barrier					144 102		0.47%		378 ways
cattle_grid					85 148		0.28%		194 ways
kissing_gate					47 408		0.15%		104 ways

(edited to correct link)

[SomeoneElseOSM]

One more question - with regard to the occurrences of linear barriers worldwide, where would be a reasonable cutoff for the number of uses to be considered?

Many more beyond the list above have more than 1k usage on ways worldwide? Is there any reason why https://taginfo.openstreetmap.org/tags/barrier=avalanche_protection , with 7k uses, shouldn't be included?

[joto]

In my opinion the number of occurances of a tag in OSM data isn't that important. What's important is how useful it is for "common maps". Shortbread is a minimal style for creating maps that are useful to lots of people. We'd be failing our mission if it becomes just a collection of popular tags. Style makers must be able to understand and deal with the data that's in the tiles. Most map makers probably don't want to style 20 different kinds of barrier. There must be some way of usefully grouping the tags to actually help style makers, otherwise we'll just produce a lot of dead data that style makers will ignore.

[SomeoneElseOSM]

In my opinion the number of occurrences of a tag in OSM data isn't that important. What's important is how useful it is for "common maps".

I'd absolutely agree with that. In the top 10 values for highway is street_lamp (5 million of those), and I'd completely understand why you wouldn't want to make larger vector tiles just to hold the positions of those, when most data consumers probably won't bother showing individual street lamp locations.

However, some of the possible values, like avalanche_protection, may be "locally very important" but a smaller number of uses globally. A map style doesn't have to show everything in Shortbread vector tiles; it might just show walls, hedges and fences or it might ignore barriers altogether. The vector tiles won't be that much larger because 7k avalanche_protection are in there globally, so non-consumers won't be inconvenienced that much.

Clearly there has to be some cut-off between "values we care about" and "values we don't"; I was just trying to work out where that was.

[pnorman]

I've been trying to group the values into reasonable groups.

The first is some kind of gate that opens and closes

• gate
• wicket_gate
• lift_gate
  271k uses

The second group is barriers you can't see or walk through

• wall
• hedge
• retaining_wall
• city_wall
  11M uses

The third is solid raised barriers you can see through or is not normally tall enough to obstruct sight

• fence
• guard_rail
• jersey_barrier
• handrail
• chain
• rope
• cable_barrier
  9M uses

The fourth is some kind of obstacle you can walk around

• bollard
• block
• log
• planter
  70k uses

Ditch and berm don't seem to neatly fall into this and might belong in a different layer. I'm not including kerb and kerb-like features.

My initial inclination is to have the second and third groups with an attribute like solid=true|false

[joto]

My initial inclination is to have the second and third groups with an attribute like solid=true|false

Maybe we should require at least one style implementing this as a way of validating that these are useful distinctions from a cartographic viewpoint that can be implemented in the real world.

[pnorman]

@westnordost, do you have any thoughts on this?

OpenStreetMap Carto has different renderings for hedges, city walls, and all other barriers.
The Humanitarian HDM style has different renderings for barrier=gate, barrier=fence, barrier=hedge, and barrier=wall
Guru Maps Landscape has a difference between wall, fence, and hedge and do not render bollard
All Guru Maps offline maps have barriers rendered the same
StreetComplete has no differences between wall and fence.

[westnordost]

I've read your comment last week, and it sounded good.

However, you are right that StreetComplete does not distinguish between wall and fence, because both are the same from the point of view whether you can pass through or not. I think this is an important distinction to make. A normally-abled person can step over a guard rail, a cable barrier, a handrail and a jersey barrier, but a fence is (potentially) as much a barrier as a wall. That would be important to see on a map.