On 25/05/18 15:00, Nick Bolten wrote:
If I understand this proposal right, the goal of this tag is to
provide more specific information for the general likelihood of
whether a water feature (only rivers?) exists: when it comes and goes
every days.
The tag provides mapper a way of tagging rivers and streams that is
presently not available.
This sounds like there are two pieces of information that are
desirable to map:
- What is the frequency of flow/presence?
That will vary .. year to year and decade to decade ... to much change?
- Does this frequency vary over seasons?
This too will vary.
These seem like questions that deserve separate tags, for flexibility,
and could benefit from a 'subtag' approach. Let's say you want to
describe a river that always has current in the spring and summer, is
intermittent in the fall, and has no flow in the winter. This could
look like:
intermittent=yes;ephemeral;no
intermittent:ephemeral=autumn
intermittent:yes=winter
intermittent:no=spring;summer
Intermittent does not equal ephemeral.
At present in OSM the tag to indicate an intermittent flow that only
occurs in winter is
intermittent=winter
The proposal for ephemeral flow in autumn would be
ephemeral=autumn
Combining these would give
intermittent=winter
ephemeral=autumn
I would think that is easy enough to understand and matches the present
tagging scheme in use.
The first tag declares the frequency, but doesn't specify when each
tag applies. The other 3 describe how this frequency varies over
seasons. The presence of more than one value for `intermittent` would
be a hint for incremental mapping/QA: there should be one
`intermittent:<value>=<season>` for every value in `intermittent`.
Tagging a single water feature as always `ephemeral` would also be
simple and get combined with the seasonal tag:
`intermittent=ephemeral` `seasonal=<season>`.
The intermittent tag already exists .. do you want to change it?
And what if the stream has a seasonal flow in say winter and an
ephemeral flow possible in spring?
For this proposal this would be tagged
seasonal=winter
ephemeral=spring
I also have a follow-up about the use cases for this data. For
example, for the cases I can imagine off the top of my head
(scientific, humanitarian), it's valuable to know how stale the data
is, how the person collecting it determined the value (memory, general
impression as a local?), and ideally have a yearly report of flow (in
some form or another), and so a wikidata key or external db may serve
your use case better. Unfortunately, this raises a lot of hard
questions about linking OSM and time series data that I don't think
are solved, but it the discussion could be valuable in itself.
The same can be said for roads. how stale is that data .. etc.
The present tagging has no entry for ephemeral. None.
If you want more data .. such as flow rates .. then put it forward. It
would need to include perennial flows, as well as seasonal, etc.
I don't think anyone wants that data in OSM ... yet.
Nick
On Mon, May 21, 2018 at 3:35 PM Warin <61sundow...@gmail.com
<mailto:61sundow...@gmail.com>> wrote:
Hi,
Following from the discussion on "Seasonal, intermittent, and
ephemeral
water tags" I have created this proposal.
Hopefully the definition is tight enough that it excludes
intermittent,
seasonal and any other thing that is not ephemeral.
I have also included a guide on determination so that mappers can see
how to determine if something is ephemeral.
So here it is ...
https://wiki.openstreetmap.org/wiki/Proposed_features/ephemeral
Is it clear? Do you understand it?
Would you use it? If so where?
Any thing else?
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