[Tagging] How to tag small canals?

[Christoph Hormann]

On Thursday 16 August 2018, SelfishSeahorse wrote:
> Hello
>
> What is the usual (or sensible) way to tag small canals like mill
> races (example: [^1]) or small irrigation channels (example: [^2]),
> i.e. the small equivalent of waterway=canal?

A bit of information on current meaning of artificial waterway tags:

waterway=ditch and waterway=drain are largely used without a well 
defined difference between them.  In terms of documented meaning 
waterway=ditch is more for features collecting water while 
waterway=drain is more for features transporting water.  But this is 
not a difference you can find consistently being made in actual 
mapping.  Both tags were invented and are primarily used for waterways 
removing undesirable water.

There is also some minor use of waterway=ditch and waterway=drain for 
smaller natural waterways because it is rendered slightly thinner than 
waterway=stream in the standard style but this is generally accepted to 
be abuse of the tags.

waterway=canal is essentially for all open artificial waterways that are 
not primarily for transporting away undesirable water (which would be 
waterway=ditch or waterway=drain).  However since the standard style 
renders it in a fairly prominent form with a thick line smaller canals 
(like for irrigation purposes) are often tagged differently 
(waterway=ditch, waterway=drain or waterway=stream) despite not 
qualifying as such.  Still waterway=canal is the corrent tagging here, 
nothing except the standard style suggests a lower size limit for 
waterway=canal.

All of this together has its origin in the fact that in the UK and other 
early OSM countries large artificial waterways are almost always for 
navigation and small artificial waterways are almost always for 
transporting away undesirable water.

Long story short: My recommendation would be tagging waterway=canal and 
specifying usage=* and width=*.  This might not look ideal on the map 
but will allow all data users to correctly interpret the data.

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