[Tagging] convert imported natural=rock areas to bare_rock

[Friedrich Volkmann]

On 12.07.2014 01:01, Martin Koppenhoefer wrote:
>> Am 12/lug/2014 um 00:27 schrieb Friedrich Volkmann <bsd at volki.at>:
>>
>> My proposal
>> http://wiki.openstreetmap.org/wiki/Proposed_features/natural%3Drock_cleanup
>> has been in RFC state for a year
> 
> 
> Maybe a whole year is a bit long...
> 
> 3 comments:
> - you write natural=bare_rock is about rock as the surface material, so I think this would better fit in the keys "surface" or "landcover"

That's how natural=bare_rock is defined ("areas made principally or mostly
of solid rock"), analogous to natural=water/sand/grass/glacier/etc. all of
which are about the surface. The bare_rock proposal was approved 2 years ago
and there are 64 566 occurrences by now.

> - the distinction between stone and rock as the latter being firmly attached to the bedrock might often be difficult to verify on the ground

When in doubt, tag what seems most certain. That's natural=rock in most
cases. Estimations and guesses are daily business in mapping. Like guessing
tracktypes and landuses when mapping from arial images.

> -I don't like that "rock" can mean one rock or a group of rocks with at least one of them attached.
> If we are to bring in more detail, why not distinguish between one rock and a group of rocks?

See the last picture in my proposal. Is it one rock or two? You cannot tell,
because there are firmly attached to each other. If you map 2 rocks, how do
you tag the name? The name "Franzosenstein" belongs to the whole rock
formation alltogether. There's also a formation of 7 rocks called "7
Kurfürsten". It would be highly impractical to map them separately. This
kind of micro mapping should be possible, but not obligatory.

> And shouldn't from the group of rocks those that are not firmly attached to the ground be tagged "stone" according to your proposal and hence left out if the rock-tag?

You surely know the German term "Wackelsteine". A wackelstein consists of
one bottom rock connected to the ground, and one or more (more =>
Doppelwackelstein) rocks on top. They are commonly considered one single
rock formation, and therefore it should be one single object in OSM as well.
I use to map them as natural=rock, not stone, because the formation as a
whole is connected to the ground.

According to its wiki page, natural=stone is "a single notable freestanding
rock". This obviously does not apply to wackelsteins, because they are
neither single nor freestanding.

natural=stone is mainly intended for erratics, which are almost never
accompanied by rocks connected to the ground.

-- 
Friedrich K. Volkmann       http://www.volki.at/
Adr.: Davidgasse 76-80/14/10, 1100 Wien, Austria