On 25/05/18 20:09, Nick Bolten wrote:
> The tag provides mapper a way of tagging rivers and streams that is
presently not available.
> That will vary .. year to year and decade to decade ... to much change?
> This too will vary.
I think something might be getting lost in translation, since those
questions were rhetorical. I'm describing my understanding of the
proposal as it exists on the wiki, hoping it matches the intent.
> Intermittent does not equal ephemeral.
I now understand that after reading a few reviews, but the wiki
proposal does not make that very clear. From the wiki articles, an
ephemeral body of water "is only present for short duration", and
intermittent "is used to indicate that a body of water does not
permanently contain water". From those definitions alone, I'd assume
that a river could have both `intermittent=yes` and `ephemeral=yes`
and be perfectly valid. However, my new and improved understanding of
hydrology definitions would say these are separate and incompatible
categories of rivers/streams. Page 6 of this EPA document [1] has
definitions that make these things clearer, maybe a similar approach
could be taken with the wiki.
The proposal clearly says under 'definition'
"A property key for water that is only present for short duration.
‘Short duration’ is typically less than 1 day for each flow. The
majority of the time, at least 90% of the time, the water is not present."
The key thing for ephemeral is 'short duration' ... and 'dry most of the
time' ... those words do not exist for 'intermittent' nor 'seasonal' in
the OSM wiki.
> At present in OSM the tag to indicate an intermittent flow that only
occurs in winter isintermittent=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.
This is actually undocumented, and taginfo has no examples of seasons
being used as values for the `intermittent` key. With that said, I was
also suggesting that seasons might more appropriately be values for
keys describing "frequency/type of flow" like `intermittent` or
`ephemeral`, rather than having a separate `seasonal` tag, due to the
ambiguity of having more than one flow mode over the duration of a
year. Something like `intermittent:seasonal=<season>` might also work.
Maybe I'm missing a proposal for seasonal values for `intermittent`?
The key 'intermittent' is poorly defined.
I am not proposing to alter that here (I have another thread on
seasonal, intermittent and ephemeral, suggest that be used for that kind
of discussion).
The idea I'm proposing is that there may be a 'catch-all' key that
describes the 'type' of thing that `ephemeral` or `intermittent` are,
and to set `intermittent`, `ephemeral`, or otherwise (`perennial`?)
values when appropriate. What about `flow=ephemeral` or
`flow=intermittent`? Then, if you need to set more specifics, you
could use `flow:ephemeral=winter`. This also provides a convenient
hint for what is being described: the flow type of the stream.
1) these keys can also be applied to lakes .. where 'flow' is not what
is wanted.
> The intermittent tag already exists .. do you want to change it?
I think we're both considering changes to the `intermittent` tag as
potential options.
> 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
This is super confusing. Namely, the `seasonal` tag's documentation
indicates whether the feature is present, but in this case it seems to
be indicating that there is a 'full' flow
No.. is says water is present .. not quantifying the rate of flow or the
depth of water in a lake. It says water is present ... nothing else.
I can see nothing in the OSK wiki for seasonal that says it is full
flow. Or any set flow rate.
There is no proposal to tag flow rates .. if you want to do that you
propose it.
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