Changeset: 35616357
Retagged bogus motorway junction tags on those odd numbered junctions in Dublin city. Where feasible, retagged as highway=city_junction in case somebody finds some use for them. motorway_junction is harmful for both navigation hints and map display.
Closed by mackerski
Tags
created_by | JOSM/1.5 (8800 en) |
---|---|
source | bing |
Discussion
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Comment from GerdP
Hi there!
Please explain this change. My understanding is that motorway_junction was correct. -
Comment from mackerski
Hi. It's not correct - the motorway_junction tag is only appropriate for an exit from a controlled-access road (doesn't have to be a motorway). Everything about the tag is intended to be interpreted by, say, navigation systems, as a routing decision point where the only action is to exit, usually to the left (or right, depending on country). Likewise, rendered maps interpret the tag as something that should be displayed prominently even when zoomed out aggressively. Keep in mind that, for most of these junctions, it is in any case impossible to apply the tag highway=motorway_junction, since highway=traffic_signals is already in place. A strong clue that this tag was never intended for a traffic situation of this kind.
The Dublin city through route scheme is a bit of a misfit anyway for digital maps and especially for machine navigation, since it's essentially intended to solve a navigation problem manually (signs on the ground and printed maps depicting the routes). It's not clear that a user of machine navigation should even care about those routes or junction points. But if it is appropriate for us to map them, we need to do so with some assumption of use case. How will software or map renderers want to use this? I adopted the highway=city_junction tag as a way of retaining the information captured by those mappers who did the existing work until we can work out what we actually want it for. But even that tag isn't satisfactory, because of the traffic signal conflict I mention above. In reality, I think the key to managing this properly is to define a route relation for the circular routes, with the junction nodes being included in the relation with a suitable role ("junction"?). A relation is surely the only way to go for a bunch of other reasons too. Even the ref tag causes us problems - when you have highway=traffic_signals, ref=J42, doesn't it seem like this should be the ref for the signals?
So this is where I'm coming from. I'm happy to discuss any valid use cases for this data, because without doing so, I fear we will not work out a useful tagging schema.
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Comment from GerdP
OK, I agree that motorway_junction is not
really good here. A few days ago there was a discussion about named junctions,
http://gis.19327.n5.nabble.com/Named-junctions-tt5859074.html
so I suggest to use highway=junction instead. -
Comment from mackerski
The bit problem with this idea is that most of these particular junctions already have a highway tag set, highway=traffic_signals. And what we realise, I think, is that the status of these nodes as junction points on this particular route is not their primary purpose, making it problematic to set a highway or ref tag specific to this one secondary purpose. This is why I'm convinced that a route relation is the correct way to solve this (though even this has challenges in how to tag, say, the junction refs).
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Comment from GerdP
I have no idea what these ref=* on the nodes mean.
I found 79 nodes with a ref that starts with
"J" in Dublin. Some have the same ref,
some numbers are missing, for example J78 and J80 exist, but J79 doesn't.
52 are highway=traffc_signals
14 are highway=city_junctilon
the others only have the ref tag.
Nodes (1-20 of 24)
- 1
- 2
- J27 (104517946), v8
- J72 (12117928), v9
- J28 (12117934), v8
- J25 (12428431), v9
- J71 (1294904418), v4
- J37 (20299837), v8
- J45 (26189923), v7
- J56 (29396438), v9
- J78 (31054551), v11
- J52 (32335036), v5
- J53 (32335290), v8
- J57 (32336034), v9
- J26 (3648809373), v2
- J14 (3648809377), v2
- J13 (3648809378), v2
- J51 (3649018929), v2
- J44 (3649018930), v2
- J62 (3649018932), v2
- J63 (3649018933), v2
- J70 (3649018934), v2
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