On 04/13/2013 04:21 AM, Kytömaa Lauri wrote:
Martin Atkins wrote:
Refine the basic railway=* tagging to have a more specific definition,
taking inspiration from the tagging conventions around highway=* .
IMO this is flawed in two ways:
- on empty highways, one can drive in circles on the whole road surface (not that one may
or should, but they can). For anything that moves on tracks, the switches are the only
place one can change course. This makes the individual tracks and their connectivity
"the network", that is the roads they happen to run on are not the network
itself. Drawing a single way where there are multiple tracks is not wrong, but it's just
an intermediary solution before somebody has the time to add the switches and separate
the tracks.
While this is true from the perspective of the railway operator, I would
argue that passengers of the railway perceive it a single "road" where
they travel in terms of the route relations placed on top of it, not in
terms of the physical track layout. When I ride on a railway, I don't
care about where the switches are, I just care about whether the train
will stop at the two stations I'm interested in (in the correct order!)
and whether the route it's going to take is a sensible one in terms of
distance.
I agree that the next level of detail can be mapped too, but I don't
agree that level of detail is interesting for the common cases of
routing that schematic mapping is aimed at, for members of the public.
Therefore it should be handled via a separate set of tags, just as
highway tagging has a progression of tagging detail from the basic ways,
to the individual lanes, to the actual area occupied by the roadways,
with each "layer" complementing the previous rather than conflicting
with it.
and more importantly
- there are an abundance of places where the tracks switch from the simplest case "in the road" to short (or long) bits where a separate way is required ; that is, for example where the tracks diverge from the lanes and a stop platform is between the tracks and the lanes for other motorized traffic. Were the adjoining simple case ways just one tag on the road, you
would introduce arbitrary(!) turns and kinks in the course of the tracks.
Someone (you?) noted this on the talk page too, and I updated that
example to talk about the platform, but I'm not sure this example is
specifically about railways... even if the railway weren't there and the
platform were for boarding a bus (a situation which also occurs in San
Francisco) it would still be necessary to split the highway if one
wished to show the platform location; if we were to just draw the
platform next to the separated tramway without splitting the highway, it
would be unclear that the platform is within the roadway at all, just as
it would be unclear whether the tramway is in the roadway.
> Other variations exist, too. There's an example of such kink in your
proposal's example photos, the one where the two tracks suddenly come
together when they go into a tunnel.
Assuming you're talking about the rendering example I showed [1], I
considered that case an example of two mappers with different opinions
about how railways should be mapped, rather than a necessary kink in the
railway; I was using it to illustrate the idea that the lack of detailed
guidance on how to tag railways has caused differing approaches in
different places.
Tracks shown "outside" the highway where they are not, is just a rendering
issue in one map, at extreme zoom levels.
Rendering is just one symptom of the inconsistency between railways and
highways. Another symptom is that e.g. level crossings get tagged twice
-- once for each track -- even though they operate as one autonomous
unit that only risks stopping the traffic once. This can have an impact
on automobile routing.
There's already tram:lanes=yes| etc. as an additional attribute tag on the highway way to
say "the lanes of this highway contain tram tracks, which may well be drawn
separately".
I was only able to find what you described on a proposal page on the
wiki[1], but in the following form that seems compatible with my proposal:
railway:lanes=|tram|tram
direction:lanes:forward=backward|backward|forward
direction:tram:lanes:forward=|both_ways|both_ways|
[1] http://wiki.openstreetmap.org/wiki/File:Doublewaytram.png
[2]
http://wiki.openstreetmap.org/wiki/Proposed_features/lanes_General_Extension/ProposalPreVoting
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