[OSM-talk] Tagging hierarchies (was: RFC - lake)

Frederik Ramm frederik at remote.org
Sat Jan 12 13:13:04 GMT 2008


Hi,

> The world has an infinite diversity and we can't go inventing new tag
> combinations for all of them. We need to think hierarchically, start
> with the real defining characteristics: land/sea/road/rail/etc and use
> subtags for the finegrained stuff. 

While this is true, it would not be necessary to stuff the hierarchy
into the tagging scheme.

Suppose you say something like this (just an example, not meant as a
suggestion for real-world use):

1st level: natural=water
2nd:       water=standing (as opposed to flowing)
3nd:       standing_water=lake (as opposed to puddle, reservoir...)

and I suppose biologists will have a number of additional levels. 
 
What you're saying would now amount to copy this hierarchy into every
single body of water by tagging it natural=water,water=standing,
standing_water=lake,... - just so that a renderer knowing only of
natural=water can still render it.

Obviously this makes it easy to understand if you see the object out
of context, and makes it easy for the renderer. But this is at the
cost of storing the hierarchy a thousand seperate times in the
database, with a high potential for errors (something tagged
natural=forest and standing_water=lake would show up green on some
renderers and blue on others, depending what level they look at...)
and also considerable workload should the hierarchy ever be changed.

Keeping the hierarchy *external*, say on a wiki page that defines
that everything tagged "standing_water=lake" is also "water=standing"
and everything that is "water_standing" is also "natural=water", would
require only *one* tag on the object; the renderer would have to load
the hierarchy from the external source but that would really not be
too difficult.

Bye
Frederik

-- 
Frederik Ramm  ##  eMail frederik at remote.org  ##  N49°00.09' E008°23.33'





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