[Tagging] Mapping of Subway Stations

Ilya Zverev ilya at zverev.info
Mon Sep 25 07:46:32 UTC 2017


Hi Michael,

> Am 2017-09-24 um 10:49 schrieb Ilya Zverev:
>> 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?

The proposal indeed does not introduce any new tags. But it proposes a 
tagging schema that has not been documented anywhere in the wiki. I 
framed it as a proposal to get opinions of other mappers and to make it 
a written standard on metro mapping, so I could link to it people who 
map their subway.

Also it would be a handy guide for software authors that want to make 
use of our data. Having looked at the state of metro systems, I can 
safely say that no single app had been using our subway data for 
anything but highlighting ways in route relations.

> 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.

Why should it? The railway=light_rail page does enough answering, and 
the distinction is usually clear on subway maps.

> 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).

Great, you are doing a good job. But don't you think this is like saying 
"why are you mapping that city when you should be mapping this one"? I 
am interested in subway mapping, and unlike any other mode of 
transportation, it is very complex, so I decided it needs to be 
described on a single page, with links.

> 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?

Nope. Nobody declared it dead, people just forgot about it. Somebody 
simply merged stop_area and stop_area_group into a single stop_area 
relation, and subsequently people started making 100+-member stop_areas 
with EVERYTHING. It does not make using these simpler.

I am okay with having a mess for stop_areas for overground transport, 
but underground infrastructure has to be more... structured.

>> 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)

We in maps.me are currently working on public transport routing, 
starting with subways. And using the data for subways proved to be 
harder than the public transport schema suggested.

> 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.

Okay, thanks, changed that. Though we don't have many mappers with laser 
distance meters, right?

> 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.

Okay, clarified this in the proposal.

> 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.

And I think, subway mapping is exactly the case where stop_area_group 
relations are useful. Because not each of 157 metro systems has an 
openly licensed GTFS feed providing these virtual connections. And it is 
not hard to provide these in OSM, just by creating stop_area_group 
relations. You cannot derive these from footways either, because only a 
few cities have that thoroughly drawn stations, and even these are not 
mapped consistently. This task is definitely not solvable by a computer 
programme — believe me, I tried. Had to do a lot of manual fixing 
afterwards.

> Suggestions are non-factual information which do not fit into
> the goals of OpenStreetMap which is based on facts.

Interchanges are not suggestions, they are clearly defined in the 
proposal and quite prominent on any subway maps. With your arguments you 
can build a case for dismissing stop_area relations, and also highway 
route and waterway relations.

Ilya



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