[Tagging] Feature Proposal - crossing=marked

[Nick Bolten]

> If there is not any control of the crossing...yes otherwise should be
crossing=traffic_signals or supervised=yes as you can read in the wiki.

But the meaning of "control" varies by region and municipality, and does
not imply the presence or absence of ground markings. A controlled crossing
can have or lack ground markings, and an uncontrolled can have or lack
ground markings.

> Well, in my country it is, when there is a traffic signals with
pedestrian traffic signal there is a crossing=traffic_signals. Otherwise is
crossing=no because there is no crossing at all.

In your country, how do you map a crossing that has traffic controls but
does not have markings on the ground?

> Change the questions:
> -Is there any traffic signal in the crossing?
> -Is there any supervision in the crossing?
> -Is there any mark in the crossing?

I don't know what it means for a crossing to be supervised, but I do like
the others you've listed. I would prefer that the crossing=* tagging schema
reflect the questions you are asking, they're the right ones for
pedestrians. What I'm saying is that the current OSM schema seems to ask
the questions I listed, but they get described by a single value like
"uncontrolled", to the confusion of all. In other words:
crossing=uncontrolled implies at least 3 pieces of information. Imagine if
we instead had a schema for your questions that looked something like this:

crossing:traffic_signal=yes/no/*
crossing:supervision=yes/no/*
crossing:marking=yes/no/* (or crossing=marked/unmarked/*)

That would be separating those questions out much better than the current
schema and be much easier to map.

> No , for a pedestrian way which passes inside an island I have
footway=crossing because there si a footway inside a island. I don't need a
tag which says things I can see in the situation for the map. It is the
same reason I don't need crossing=marked if I have crossing=uncontrolled.
Mark is not a control.

While it is not as thoroughly-documented as it could be, the wiki states
that crossing:island can be applied to the footway:
https://wiki.openstreetmap.org/wiki/Key:crossing:island. Specifically, "or
alternatively on a pedestrian crossing way highway=footway +
footway=crossing".

As an example, imagine that you are a data consumer and you want to tell a
pedestrian router that they are using an island. If you were to look up a
crossing:island key on a given footway, you could tell them, "use a traffic
island to get to <whatever>". You can, of course, also use an advanced
router that extracts crossing:island from a node.

> Well, we have it and it is called crossing_ref.

crossing_ref is not actually a tag for noting the type of markings, nor was
it intended to be. It's a dumping ground for the older UK-centric tagging
schema that used zebra, toucan, pelican, etc, with those UK-specific
right-of-way implications. For example, crossing_ref does not have a
"ladder" key, even though that's an extremely common marking type:
https://taginfo.openstreetmap.org/keys/crossing_ref#values. As you can see,
pretty much all of them are just "zebra". Many people from the UK get
annoyed when you call a US-based ladder crossing a "zebra crossing", as our
ladder crossings do not have the same right-of-way implications nor the
angled markings.

> I was talking about crossing=zebra issue.

Ah, I see. I just misunderstood, my fault.

> Tell me one situation you cannot map in detail with present tagging
scheme.

* Map a crossing that is unmarked and has pedestrian signals ("walk"/"do
not walk").
* Map a crossing that is marked and is protected by a stop sign but no
traffic light, then say how you would interpret this as a data consumer.
* Map a crossing that is unmarked and is protected by a stop sign but no
traffic light, then say how you would interpret this as a data consumer.
* Map a crossing that is unmarked and is protected by its own,
non-street-intersection traffic light, then say how you would interpret
this as a data consumer.
* Map a crossing that is unmarked, has pedestrian-specific signals
("walk"/"do not walk"), but no traffic signals at all nearby.
* Map a crossing that has markings and is protected by a traffic light, but
that traffic light is part of the overall highway=traffic_signals
signalization, not specific to just that crossing.
* Map an unmarked crossing that has the same type of traffic light
situation: the light is to stop traffic at the intersection, not that
particular crossing alone. Map an unmarked crossing that has
pedestrian-specific signals ("walk"/"do not walk") and has that same
"intersection-only" traffic light.
* Map a marked crossing where pedestrians lack the right of way.
* Map an marked crossing that has dropped curbs (keep in mind that some
veteran OSM mappers have stated that dropped curbs are a control).

I have no doubt that you can come up with some examples that *mostly* work.
But they will be ambiguous to a data consumer and often most mappers.

Best,

Nick
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