[Tagging] tag groupings

Tobias Knerr osm at tobias-knerr.de
Sat Jul 31 03:40:09 BST 2010

First, I want to add some more arguments to the list:

@ Cons "Defined groupings approach"
- sometimes meanings will be read into a key that originally weren't
there(1), this cannot happen with a generic type key

@ Pros "All in one approach"
- it's easier to find the correct tag if it *does* use the value you
expect, because you don't also need to identify the correct key(2)

Examples can be found in the footnotes of this mail.

But I'm not even convinced that the main advantage claimed for the
groupings approach has much practical relevance in the first place:

Stephen Hope wrote:
> Defined groupings approach
> Pros
> - by having a things in more defined groups, it's easier to have
> default rendering if you don't understand what the value means.  EG
> amenity=karitane_centre tells me very little, health= or medical= at
> least tells me it's health related.

For a start, consider that most maps will not attempt to display
everything. In fact, popular renderings like the Mapnik layer on osm.org
are somewhat picky when they choose which features to render, even when
it comes to well-defined tags. I don't expect the use case "renderer
that shows *everything* on the map" to be very common.

But even if a renderer wants to display features it doesn't know (and we
also don't care about the obvious disadvantages of using the exact same
"health" icon for, say, a hospital and some defibrillator box on a
wall), I question whether using a generic "health" is a significant
improvement over a generic "POI" icon.

And, of course, the keys are completely useless for those applications
that disagree with the keys' inventors on how features should be
categorized. If there was a single obvious categorization that everyone
would naturally use, then we might consider implementing that one. But
this is obviously not the case.

Tobias Knerr

1) natural=wood, for example, only later was clearly defined as the
"untouched nature" tag that it is now - which was a somewhat definition,
because many had considered it just a generic tag for woods and used it
as such. Using either type=wood (+ natural=yes/no) or type=natural_wood
would have prevented any confusion in this regard.

2) keys are far from obvious. The "Defined groupings approach" crowd has
so far proposed at least "medical", "healthcare" and "emergency" as keys
for "hospital". And with proposed, I mean "discussed in at least one
lengthy mailing list thread and/or documented it on the wiki".

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