> On Jan 15, 2015, at 6:13 PM, Christoph Hormann <chris_horm...@gmx.de> wrote:
>
> On Thursday 15 January 2015, johnw wrote:
>>
>> A wadi is a place where flash floods occur. It is not an intermittent
>> river - it isn’t really seasonally wet, and doesn’t provide any real
>> expectation that water will be present (except deep underground) -
>> because they are located in places where rain itself is unexpected
>> for most of the year.
>
> Well - that would be a useful concept of a wadi but it has two problems:
>
> * current use of the tag is very different from that, you can see that
> quite well when you look at the taginfo map:
>
> https://taginfo.openstreetmap.org/tags/waterway=wadi#map
>
> the uses in Europe for example are probably almost always seasonal.
> * sporadic waterflow is very difficult to determine for the mapper.
> This is especially true for northern Africa where climate got a lot
> drier in the last few thousand years and as a result there are many
> permanently dry valleys that still look like being formed by waterflow
> but that have not seen significant waterflow in the last hundred years.
>
> My suggestion would probably be to stop rendering waterway=wadi in a way
> implying waterflow, encourage mappers to use intermittent/seasonal
> where this is known and reserve waterway=wadi - despite the then
> misleading key - for valleys where waterflow is unknown.
>
if it is the case that wadis are
- not following my definition of a wadi
- not currently tagged on wadis
Then spitting off waterway=wash is the best idea, because
- it is a defined geographic feature
- is labeled and well known in the regions they exist, and are easy to tell
apart to regional mappers.
- and most importantly (to me) has a much different connotation than
“intermittant stream”
- more accurately describes the world as it exists.
However all those tags in Africa and the Americas are probably correctly tagged.
I bet cleanup of this tag will require some re-tagging, or a much broader
definition of wadi - which would turn it into an intermittent or seasonal
stream/river, so what’s the point of having the tag then…
thanks for the useful data/map.
> --
> Christoph Hormann
> http://www.imagico.de/
>
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