[Tagging] Mapping of Subway Stations

[Michael Reichert]

Hi Ilya,

Am 2017-09-24 um 10:49 schrieb Ilya Zverev:
> I had a task of extracting subway infrastructure from OpenStreetMap, and
> I found out that some things cannot be mapped at all (e.g.
> interchanges), and some are unclear or mapped differently in different
> countries.
> 
> Please consider this proposal that clarifies tagging and mapping of
> subway stations:
> 
> https://wiki.openstreetmap.org/wiki/Proposed_features/Metro_Mapping

I don't understand what's the aim of your "proposal". There are almost
no new tags. Is it intended as a write-up of what could and should be
mapped and tagged and how that should happen?

It is a good write-up, it gives a good overview but does not answer the
questions of the differences between railway=subway, railway=train,
railway=light_rail and railway=tram.

I am not against a long and structured write-up for mapping public
transport but I would prefer if people would invest the time into
cleaning up existing pages on the wiki. There is already an overview
page: https://wiki.openstreetmap.org/wiki/Public_transport
I started cleaning it up (based on the German version which was cleaned
up and reviewed more than a year ago).

> I have already started improving the mapping of several metro systems in
> different cities. Mostly that involves adding stop_area and
> stop_area_group relations.

I thought that stop_area_group is a dead branch of the "Oxomoa" public
transport tagging scheme which influenced the current tagging scheme (I
prefer the term PTv2 – Public Transport version 2 – for it), isn't it?

> Adhering to this document would greatly simplify using subway data from
> OpenStreetMap in applications — both for multi-modal routing and for
> formatting pretty schemes.

That's a goal everyone had who wrote a tagging guide or proposal for
public transport. The key problem is a lack of guidance by tools using
the data. While other topics have lots of map styles/routing engines and
quality assurance tools, public transport has only very few tools which
are up to date and still maintained. (I currently work on public
transport validator)

https://wiki.osm.org/wiki/Proposed_features/Metro_Mapping writes:
> If you know the location and length of a platform for a subway station, map it as a way Way. Using a node is pretty meaningless, and drawing a platform as an area is an overkill, though possible. You can see an example of such thoroughly drawn platforms here. 

A way is better than nothing but if a mapper is able to draw an area
because the station is pretty simple or he used a laser distance meter
[1], this should not hinder him to draw an area.

https://wiki.osm.org/wiki/Proposed_features/Metro_Mapping writes:
> The modern public transport tagging schema introduces stop positions: points on rails where trains actually stop. These should be placed in the middle of a hypothetical train, that is, near the center of the platform.

Adding them always near the centre of the platform is wrong and useless.
A machine could that do, too. From my point of view they should be added
where the centre of the train is. If a platform is three MU long but
trains are only three MU long during peak hours and short trains stop
near one end of the platform, the stop position node should be located
where the centre of the shortest train will be. Many train, tram, subway
and light rail systems have signs in the track or along the track which
tell the driver where to stop depending on the length of his train. This
signs can also be used by mappers and passengers who know how to
interpret them.

https://wiki.osm.org/wiki/Proposed_features/Metro_Mapping writes:
> When it is possible to go from a station to another station without leaving the metro system, that is, without passing a railway=subway_entrance node, these stations are considered to be in an interchange. To mark it, create a public_transport=stop_area_group relation, and add stop_area relations (not station nodes!) of all stations that are part of the interchange. 

I am not a fan of stop_area_group relations. They tend to be collective
relations (like stop area relations). The practical use of
stop_area_group relations is limited.

Classic public transport routing engines need a manually produced set of
"virtual" connections between two stations which are within a walkable
distance, e.g. from Weinheim(Bergstraße) to Weinheim Hbf [2] because
they only calculate routes based on the timetable. Nowadays multi-modal
public transport routing engines are available, even as open source
software. That's why I think that any suggestions for interchanges
should not be mapped. It is a problem which solveable by a computer
programme. Suggestions are non-factual information which do not fit into
the goals of OpenStreetMap which is based on facts.

Best regards

Michael


[1] https://youtu.be/5T5zH-zanXI?t=10m48s
[2] https://www.openstreetmap.org/#map=17/49.55290/8.66625

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