[Tagging] How to tag small canals?

Christoph Hormann osm at imagico.de
Fri Aug 17 11:43:47 UTC 2018

On Friday 17 August 2018, SelfishSeahorse wrote:
> >
> > Yes, that was the obvious attempt to expand the narrow scheme to
> > other parts of the world in a superficial way oriented at the
> > standard style rendering but not at the actual semantics.
> Actually, it's only drain that doesn't seem to make sense
> semantically, but ditch seems to be fine for smaller canals used for
> drainage and irrigation, at least according to the definitions by
> Wikipedia[^1] and the Cambridge Dictionary[^2].

The meaning of tags in OSM however does not necessarily have anything to 
do with the meaning of the English language words used for key and 

waterway=drain and waterway=ditch were both from the beginning intended 
and used primarily for structures transporting away undesirable water.

> I'm not sure if a (smaller) mill race can also be called a ditch, but
> i think it makes sense to have at least two tags for man-made
> channels of different width.

Because that works so great for natural waterways?

I would say if you want to document the width then tag width=*.

> In my opinion the material of the lining/confine should better be
> tagged separately, perhaps confine:material=concrete/wood/....
> As for natural waterways, I could imagine the following
> classification based on width:
> * waterway=stream/brook - possible to jump across (< 1 m wide?)
> * waterway=creek - small to medium-sized natural stream (1-3 m wide)
> * waterway=river (3-10 m wide)
> * waterway=broad_river (> 10 m wide)

Somewhat off topic here - but as said you cannot change the meaning of a 
tag that is used hundreds of thousands of times.

> Of course we could just use width=*, but it's not always easily
> possible to measure the width (e.g. in a forest) and sometimes it
> changes often.

I would translate this into "i want a subjective non-verifiable 
classification system but i hide this by defining pro forma verifiable 
criteria for the classes".

If you want to map the river width tag width=*, if you don't want to map 
the width then don't create classes based on width thresholds.

Christoph Hormann

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