[Tagging] Definition of lake/pond as applied to stream/plunge pools

Tue Dec 22 13:47:48 UTC 2020

Great discussion, here and in the 2017 thread.  Participation in the
tagging list is certainly educational.

water=stream_pool suffers from a few problems, and its use seems far from a
settled question.  (None of this is meant as criticism, as I understand all
too well the hard work involved in developing proposals and good wiki
documentation).

In the three years since that discussion, water=stream_pool has achieved
just 425 usages.  I assume that the biggest reason for this is that it's
only documented as an entry in the table for the wiki page for Key=water.
Notably absent is any mention of stream pools (or for that matter, plunge
pools) from either of the two main wiki pages for river documentation
(water=river vs waterway=riverbank).  This begs the question of how
water=stream_pool should interlace with river polygons for mapping.

Stream/plunge pools are part of a river or stream (I assert this based on
Wikipedia's definition).  Logically, one might think "chop up the river
polygon, and tag the stream pool portion as a stream pool".  This approach
has a few problems:

1. If the river area is tagged with the water=river scheme, the area of the
stream pool is no longer tagged as a river (because water=stream_pool
conflicts with water=river).  This is wrong because the stream/plunge pool
is indeed part of the river.  You could use the waterway=riverbank scheme,
but now you're blending the two types of river tagging.  Yuck.
2. If the stream pool has a name, that portion of the river loses the name
of the river, as the polygon can only have one name= tag.  The
waterway=river way of course would still carry the name, so you do still
maintain continuity.  But you lose concepts like "the total surface area of
the river".

Alternately, you could overlap the pool area over the river polygon, but
then you're double-tagging the water area which seems like poor practice,
and certainly JOSM would give you a warning for overlapping water features.

It seems to me that river=stream_pool would have been the more sensible
tagging within the natural=water+water=river scheme, as it further
describes that portion of the river.

The low usage and structural problems associated with stream pool tagging
suggest that this is not a ready-for-prime-time tagging scheme, and
deserves a proposal - not just a mailing list discussion - to sort out
fundamentally unanswered questions about how to tag a river with both named
and unnamed stream pools, particularly with regard to how the polygons are
divided and/or overlapped.  One might also argue that a stream pool should
simply be mapped as a node, and if it's too big for a node, then perhaps
it's more properly tagged as a pond or lake.  Unanswered questions.

Stream and plunge pools are a part of rivers (per WP definition), and I
don't intend to address river tagging as part of the reservoir/lake/pond
proposal[1].  Therefore, what makes the most sense is to simply scrub
mention of pools and rivers from the proposal and leave it squarely focused
on reservoirs, lakes, and ponds.

[1] https://wiki.openstreetmap.org/wiki/Proposed_features/Reservoir

On Tue, Dec 22, 2020 at 12:49 AM Andrew Harvey <andrew.harvey4 at gmail.com>
wrote:

> Back in 2017 this was discussed on the list
> https://lists.openstreetmap.org/pipermail/tagging/2017-March/031595.html and
> the outcome of that was I added water=stream_pool to the wiki at
> https://wiki.openstreetmap.org/wiki/Key:water#Natural_features. Is there
> any reason to change this now? I think continuing to tag these as
> natural=water + water=stream_pool is best as currently documented and in
> use.
>
> On Tue, 22 Dec 2020 at 05:13, Brian M. Sperlongano <zelonewolf at gmail.com>
> wrote:
>
>> Discussion on the current reservoir proposal[1] (which seeks to define
>> the distinction between reservoirs, lakes, and ponds) has brought up the
>> question of stream/plunge pools[2,3], and how they fit into the lake/pond
>> definitions.
>>
>> I've come up with the following text:
>>
>> "Occasionally a river or stream will form a stream pool or plunge pool,
>> which are bodies of water that naturally occur along the course of the
>> waterway. These waterbodies may either be tagged as a lake or (usually)
>> pond if they are named or significant in size, or else they can be simply
>> conflated with the river."
>>
>> Is this distinction satisfactory?  How are folks tagging these features?
>>
>>
>> [1] https://wiki.openstreetmap.org/wiki/Proposed_features/Reservoir
>> [2] https://en.wikipedia.org/wiki/Stream_pool
>> [3] https://en.wikipedia.org/wiki/Plunge_pool
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