[Tagging] Super-keys are evil

fly lowflight66 at googlemail.com
Wed Feb 25 15:42:54 UTC 2015

Though, I have to admit that introducing new categories nor moving tags
from one to another is not easy and often bricks, like osm-carto will
not support it for quite some time, are through between your legs.

Still in favour of introducing some more categories.

cu fly

Am 24.02.2015 um 20:02 schrieb Frederik Ramm:

> On 02/23/2015 02:43 AM, Kurt Blunt wrote:
>> Right now, tags serve two distinct purposes. There are attribute tags
>> like name=Wall Street, and there are category tags like
>> amenity=parking or aeroway=helipad. 
> This works for many things but not all; the border can be blurred. You
> will not be able to fit every key into your "category or attribute" schema.
>> Many tags don't even make sense. What does highway=track mean? Is it
>> a highway that acts as a track? A track is clearly not a type of
>> highway. A track is just a track.
> And if you travel along a dark track in the night then you might be
> robbed by a highwayman.
>> A contributor is left to feel like
>> an idiot for not understanding the logic behind this system.
> Woe betide all who mistake highway=unclasssified for a street that lacks
> classification.
>> For these reasons, I believe there is a case to be made for an
>> overhaul of category tags. My personal opinion is that we should get
>> rid of super-keys altogether and instead promote all categories to
>> keys with empty values: "amenity"="reception_desk" becomes
>> "reception_desk"="", "highway"="track" becomes "track"="", 
>> "aerialway"="gondola" becomes "gondola"="", "barrier"="city_wall"
>> becomes "city_wall"="", "historic"="city_gate" becomes
>> "city_gate"="", "sport"="volleyball" becomes "volleyball"="", etc.
> And power=line becomes line="" and barrier=line becomes, uh, wait a minute.
> It is not so simple, even leaving aside the fact that many programs
> would simply dismiss your empty values.
>> Now, I don't actually think such an overhaul is currently feasible
>> given the massive burden it would put on the database system.
>> However, it might be something to think about for the future.
> I think that in theory what you call "super keys" is a good thing to
> have because it gives you a layered level of understanding. For example,
> if someone tags
> natural=water
> water=lake
> lake=turlough
> then you have a chance to understand "this is a natural feature" (and
> not man-made) even if you don't know what a lake is; you can understand
> "this is a lake" (and not a reservoir) even if you don't know what a
> turlough is; or you're so much into water bodies that you can actually
> understand the full message.
> If the tag was instead the space-saving
> turlough=""
> then you'd be stumped without recourse to the giant tag dictionary that
> explains to your renderer that something tagged turlough="" should
> perhaps be drawn in a blue-ish colour.
> Matter in a nutshell: Certainly the way we use these "super tags" has a
> lot of historical baggage but I don't think it is a stupid idea per se,
> *especially* if your goal is (like you're claiming yours to be) making
> tags easy for mappers.

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