[Tagging] Trolltags

Dave F. davefox at madasafish.com
Mon Aug 31 12:08:34 UTC 2015

Thank you for clarifying. I wanted to be sure of your meaning before 

Your suggestion of decreasing the road class is "trolltaging" Please 
don't do that. Lane closures or access restrictions etc, does not change 
a road's classification.

Please refrain from inventing words such as 'trolltag'. it doesn't help 
in discussions especially when there are people of different nations 
speaking numerous languages. It just causes confusion & doesn't make the 
inventor of the word look clever or important. Please use a word such as 
'incorrect' instead.

Dave F.

On 31/08/2015 12:41, Mateusz Konieczny wrote:
> 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
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