[Tagging] RFC proposed water property key 'ephemeral '

Warin 61sundowner at gmail.com
Fri May 25 09:15:18 UTC 2018

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 anĀ  intermittent flow that only 
occurs in winter is

The proposal for ephemeral flow in autumn would be

Combining these would give

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

> 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 <61sundowner at gmail.com 
> <mailto:61sundowner at 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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