[Tagging] Trolltags

Christian Pietzsch christian.pietzsch at gmail.com
Mon Aug 31 14:23:36 UTC 2015

That's why I would prefer a generalized life cycle tagging scheme in the
form of a prefix. (http://wiki.openstreetmap.org/wiki/Lifecycle_prefix)
For example "disused:highway=cycleway".
It would eliminate the need for data consumers to filter for more tags than
you need. If you just look for cycleways that are in use, you only have to
search for highway=cycleway (or highway=path + bicycle=designated).

I had the problem with buildings. If you use building=proposed + proposed=*
than it gets rendered on the map because everything that's building=* gets
rendered. The life cycle prefix (sometimes suffix) is used quite often if
it isn't a highway or railway.


2015-08-31 13:41 GMT+02:00 Mateusz Konieczny <matkoniecz at gmail.com>:

> On Mon, 31 Aug 2015 01:29:45 +0100
> "Dave F." <davefox at madasafish.com> wrote:
> > What's a 'trolltag'?
> It is not OK to use one tag (for example amenity=hotel) and add second
> tag that negates or massively change its meaning (for example adding
> involuntary=yes to amenity=hotel instead of using amenity=prison).
> Additional tags should clarify meaning of main tags rather than negate
> it.
> In general, any tag tag must be processed to avoid producing false or
> invalid data is a trolltag.
> For example somebody wants to produce map of cycleways. Simply
> processing highway=cycleway and highway=path with bicycle=designated
> should be enough. Data consumer in that situation should not be
> expected to check for "proposed=yes", "demolished=yes",
> "construction=yes", "completely_fictional=yes" or "end_date=1990".
> Obviously, one may want to look for more detail - for example to show
> proper map of cycleways one would want to check also access, surface,
> oneway and other tags. But again - segment of cycleway destroyed in
> landslide should be removed from map rather than tagged as
> [highway=cycleway, surface=giant_gaping_hole, smoothness=impassable].
> Adding tags like proposed=yes is a really poor idea. In case of data
> consumers not supporting them it will lead to invalid and highly
> misleading data. And data consumers supporting completely broken
> tagging schemes (like [highway=tertiary; construction=yes] instead of
> supporting just [highway=construction, construction=tertiary])
> encourages usage of this tagging method. The danger is that with more
> and more data tagged using trolltags other data consumers will either
> be forced to add support for trolltags or stop using OSM data.
> And possibilities for trolltag are endless. Lets say that somebody
> wants to display existing shops and support all tagging schemes. Good
> luck with filtering out proposed=yes, abandoned=yes, vacant=yes,
> demolished=yes, construction=yes, empty=yes, ruins=yes, parsing
> start_date and end_date etc etc.
> Some real examples:
> http://www.openstreetmap.org/way/36478401 - there was a building. Then
> it was demolished. But somebody, instead of deleting it from OSM (or
> maybe temporarily converting it into note="there was building here now
> it is demolished") decided to add demolished=yes.
> http://www.openstreetmap.org/relation/1918067 - railway=route tagged on
> highways and footways. To detect that this is not a railway route but
> original research about line that was closed over 80 years ago one
> would need to process "note=abandoned railway" or
> "railway:end_date=1931"
> In many cases (like this two cases above) correct mapping is no mapping
> whatsoever. What existed in past and is not existing now should not be
> mapped in OSM (see http://www.openstreetmap.org/welcome - "What it
> doesn't include is opinionated data like ratings, historical or
> hypothetical features, and data from copyrighted sources.").
> In other cases objects should not be deleted but retagged. For example
> in really rare cases mapping proposed roads makes sense. Maybe some
> proposal for constructing footways are also verifiable. But in that
> case use [highway=proposed, proposed=footway] rather than
> [highway=footway; proposed=yes]. At least normal data users will not be
> mislead into displaying proposals as reality. (and yes, somebody did it
> - see http://www.openstreetmap.org/way/53821342 ).
> It is OK to map objects under construction. But [highway=footway;
> construction=yes] is the best method to irritate data consumers (real -
> see
> http://www.openstreetmap.org/way/281018186#map=19/51.50653/-0.01904).
> Use [highway=construction; construction=footway] instead.
> And good luck with interpreting [construction=yes; railway=tram_stop;
> start_date=2012]. Is it construction that was supposed to end in 2012?
> Is it construction that was supposed to start in 2012? And almost
> everybody will process it as an existing tram stop. It would be better
> to avoid mapping
> http://www.openstreetmap.org/node/1049342953#map=19/53.47988/-2.15500
> until it was really constructed (or use something like
> [construction=tram_stop, end_date=2012])
> Note that some tags may be OK or trolltag depending on how it is used.
> For example abandoned=yes. It is perfectly OK to add it to building -
> after all, abandoned building is still building. But using it on
> shop=supermarket to indicate that shop is no longer operating and it is
> impossible to buy anything there (in other words - it is no longer a
> shop) is not OK and should be tagged in proper way (typically - by
> deleting shop=supermarket).
> Disclaimer - trolltags are frequently not processed and ignored. As
> result it is typical that [highway=motorway, construction=yes] is no
> longer under construction and may be used. This type of issues as
> usually requires survey on the ground to be properly fixed.
> And you may use this overpass query to detect more in your region -
> http://overpass-turbo.eu/s/bcS (it includes tags that nearly always are
> trolltags - but certainly some false positives will appear. For example
> vacant=yes is fine for building).
> Content of this mail is also posted on
> http://www.openstreetmap.org/user/Mateusz%20Konieczny/diary/35702
> _______________________________________________
> Tagging mailing list
> Tagging at openstreetmap.org
> https://lists.openstreetmap.org/listinfo/tagging


PGP-Schl├╝ssel <http://keyserver.pgp.com/vkd/DownloadKey.event?keyid=0x7E227A9D3E298033>
Version: Mailvelope v1.0.1
Comment: https://www.mailvelope.com

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstreetmap.org/pipermail/tagging/attachments/20150831/8d31a08f/attachment-0001.html>

More information about the Tagging mailing list