[Tagging] Drain vs ditch

[Warin]

It appears in the descriptions that a 'ditch' can be used as a 'drain'. 
So why have a tag 'drain'?

The only differences I have between canal and the other things is large 
verse small and usefull quantity.
Rather subjective, not a objective measurement. If the differences as so 
arbitrary why distinguish between them at all?

On 01/02/19 09:45, Sergio Manzi wrote:
>
> Yes, great descriptions!
>
> My only marginal objection is for canal: why don't you ditch (pun 
> intended...) the "/used to carry useful water for transportation, 
> hydro-power generation, //irrigation or land drainage purposes/" clause?
>
> Are there any other "/Large man-made open flow (free flow vs pipe 
> flow) waterways/" that should *not *be considered canals?
>
> My concern is that somewhere in the world there could be a canal not 
> built for any of those purposes and somebody could object to call it 
> "a canal".
>
> Also isn't "land drainage" potentially in contradiction with "useful 
> water"?
>
> Cheers,
>
> Sergio
>
>
> On 2019-01-31 23:34, Eugene Podshivalov wrote:
>> Hi Markus,
>> I find your amendments great.
>>
>> Cheers,
>> Eugene
>>
>> чт, 31 янв. 2019 г. в 20:29, Markus <selfishseahorse at gmail.com 
>> <mailto:selfishseahorse at gmail.com>>:
>>
>>     Hi Eugene
>>
>>     Thanks for your summary! [^1] I'm in favour of the proposed
>>     definitions and would welcome if the clarifications regarding
>>     size you
>>     made here [^2] were included in the definitions, like for example
>>     (*additions*, ~~deletions~~):
>>
>>     canal - Large man-made open flow (free flow vs pipe flow) waterways
>>     used to carry useful water for transportation, hydro-power
>>     generation,
>>     irrigation or land drainage purposes. Consider using waterway=ditch
>>     for small*er* ~~irrigation or land drainage~~ channels *that directly
>>     distribute water to or collect it form the land*. Consider using
>>     waterway=drain for small usually lined superflous liquid drainage
>>     channels.
>>
>>     ditch - Small artificial free flow waterways *used to directly
>>     distribute water to dry land (for irrigation) or collect water from
>>     wet land (for drainage)* ~~used for irrigating dry land or draining
>>     wet land~~. Irrigation ditches can be lined or unlined, drainage
>>     ditches are usually unlined to let water soak through the land into
>>     them. Ditches may have short lined segments at waterway turning
>>     points
>>     or intersections with roads or paths to prevent erosion. Consider
>>     using waterway=canal for large*r* ~~irrigation or land drainage~~
>>     channels *that convey water from or to ditches*. Consider using
>>     waterway=drain for usually lined superflous liquid drainage channels.
>>
>>     [^1]:
>>     <https://lists.openstreetmap.org/pipermail/tagging/2019-January/042543.html>
>>     [^2]:
>>     <https://lists.openstreetmap.org/pipermail/tagging/2019-January/042551.html>
>>
>>     Regards
>>
>>     Markus
>>
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