[Tagging] waterway=penstock to complete pipeline tagging

[Christoph Hormann]

On Monday 05 October 2015, François Lacombe wrote:
>
> What I propose : (man_made=pipeline + substance=water) +
> waterway=penstock or waterway=penstock + tunnel=yes or...
>
> A water carrying pipeline isn't always a penstock.
> A penstock isn't always a pipeline : sometimes shielded tunnels are
> directly digged in rock.

Waterway=* is traditionally only for free surface flow - even with 
tunnel=yes (although this is not generally followed strictly for short 
tunneled parts as mentioned).  The wiki does not explicitly mention 
this but it is clearly implied there.  There is no practical difference 
if a pressure tube is directly cut into rock or if there is a 
concrete/metal lining/tubing.  So IMO man_made=pipeline is appropriate 
for all of these - adding a waterway tag seems unnecessary and 
redundant unless one of the existing waterway tags applies.

> > waterway=penstock would also lack any functional distinction that
> > would normally be encoded in the waterway tag - data users would
> > have no way to decide how treat such feature.  It would just say
> > 'this waterway is tubed' not what kind of waterway it is
> > (artificial/natural, clean/dirty water etc.)
>
> waterway=canal and waterway=drain don't give those details too :
> would you be able to say if the water is clean or waste when
> waterway=canal used ?
> A penstock isn't a drain, isn't a canal or a river : it's a shielded
> tube (not always a pipe) carrying water down a mountain to obtain a
> high pressure flow. What more functional details can we give
> regarding this definition ?

Short penstocks are frequently part of a river/stream but likewise exist 
as parts of artificial waterways.  You'd loose this distinction with 
waterway=penstock.  Generally waterway=* characterizes the water and 
its flow while the term 'penstock' identifies a man made 
infrastructure.  Your tagging suggestion mixes these two separate 
concepts into one tag which can be confusing for the mapper.

-- 
Christoph Hormann
http://www.imagico.de/