[Tagging] Drain vs ditch

Eugene Podshivalov yaugenka at gmail.com
Sun Feb 10 13:57:01 UTC 2019


Short summary of what we have ended up with so far.
---------
*Variant #1*
Keep both "drain" and "ditch" tags but update their definitions to make a
clear cut between the meanings:

drain - Small artificial free flow waterways usually lined with concrete or
> similar used for carrying away superflous liquid like rain water or
> industrial discharge without letting it soak into the ground. Consider
> using waterway=ditch for unlined channels used to drain nearby wet land.
> Consider using waterway=canal for large unlined land drainage channels.

https://lists.openstreetmap.org/pipermail/tagging/2019-January/042543.html

ditch - Small artificial free flow waterways used to directly distribute
> water to dry land (for irrigation) or collect water from wet land (for
> drainage). 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 larger
> channels *that convey water from or to ditches. Consider using
> waterway=drain for usually lined superflous liquid drainage channels.

 https://lists.openstreetmap.org/pipermail/tagging/2019-January/042566.html

*Variant #2*
Combine "ditch" and "drain" tags into one.

ditch - a narrow channel dug at the side of a road or field, to hold, bring
or carry away water or industrial discharge.
(a) The purspose can be clarified by usage=irrigation/drainage attribute.
Drainage is assumed by default if not defined.
(b) Industrial discharge ditches can be clarified by
industrial_discharge=yes attribute.
(c) Lined channels can be clarified by lined=yes+liner=<material> attribute.

note: I'm not sure about the attribute names.
---------
Personally I lean toward variant 2 because
- if a drain is a digged out channel, then it is a ditch, and no need to
clarify the purpose because drainage is assumed by default
- if a drain is not a digged out channel, then some absolutely different
tags should be used like man_made=* or pipe_line=*
- if you want to specify industrial discharge drainage then you have to use
an additional attribute anyway to distinguish it from storm water drains.
- if we had a separate tag for "drains" then lined would be assumed by
default, but you would have to define lined=no attribute for unlined drains
then. This seems to be the only point which would make the life easier with
two separate tags.

Cheers,
Eugene


сб, 2 февр. 2019 г. в 19:44, Eugene Podshivalov <yaugenka at gmail.com>:

> Not all ditches can be called drains and not all drains can be called
> ditches and there is some overlapping in their meanings which causes the
> confusion.
>
> I see three ways to go:
> 1. Define the basic meanings from dictionaries and let users decide on
> which tag to use, similar to Peter Elderson's version from the preceding
> post.
> 2. Allow some deviation from dictionary definitions to make a clear cut
> between the two. This is similar to how "stream" is currently restricted to
> the maning of "you can jump over it".
> 3. Introduce some abstract notions with clear definitions of each
> sub-notion. Similar to highway=track + tracktype=grade1,grade2 etc. or
> boundary=administrative + admin_level=2,3 etc.
>
> Cheers,
> Eugene
>
> сб, 2 февр. 2019 г. в 18:48, Peter Elderson <pelderson at gmail.com>:
>
>> If there is a drain worth mapping, I will map it as a drain.
>>
>> If the drain has the form of a ditch and I can see its only function is
>> to be a drain, I will map a drain. Size and lining may be indicators, not
>> definers.
>>
>> If a ditch has unclear function or multiple functions, I will map a
>> ditch. If I think it’s worth mapping.
>>
>> I will not systematically retag drains to ditches unless the national
>> community decides to do so. Automated edits: no way.
>>
>> Mvg Peter Elderson
>>
>> > Op 2 feb. 2019 om 14:22 heeft Hufkratzer <hufkratzer at gmail.com> het
>> volgende geschreven:
>> >
>> > If we were discussing a proposal I would agree, but replacing
>> waterway=drain by waterway=ditch + usage=drainage or sth. like that is not
>> such an easy task.  We already have 800k drains. I assume it requires a
>> proposal with volting to deprecate drain, adaption of the presets, perhaps
>> a mass edit. Who will do all this? Is the advantage of using waterway=ditch
>> + usage=drainage instead of waterway=drain so immense that it is worth the
>> effort?
>> >
>> > Am 02.02.2019 13:58, schrieb nwastra:
>> >> +1
>> >>
>> >> N
>> >>
>> >>>> On 2 Feb 2019, at 10:39 pm, Markus <selfishseahorse at gmail.com>
>> wrote:
>> >>>>
>> >>>> On Sat, 2 Feb 2019 at 11:21, Sergio Manzi <smz at smz.it> wrote:
>> >>>>
>> >>>> Thank-you for confirming that, Mark.
>> >>>>
>> >>>> Personally I think we, in OSM, should stop with this folly of
>> overloading English words with meanings they do not have in any dictionary
>> (be it AmE, BrE, CaE, or whatever).
>> >>>>
>> >>>> Both the "ditch" and "drain" words can be used to describe certain
>> features in English. The difference is essentially an etymological one,
>> with one related to the process of excavation (dig -> ditch) and the other
>> to the function of carrying liquids away (dry -> drain).
>> >>>>
>> >>>> If we want to precisely map certain characteristics of a feature we
>> should do it explicitly through a correct data model that takes into
>> consideration the particular aspect we are trying to communicate. We want
>> to communicate the information that a (small) waterway is lined with
>> concrete? Just say that with an appropriate tag, like e.g. lined=*, or
>> lining=*. We want to communicate the information that a (small) waterway is
>> used to carry waste water away? Once again, let's say that with an
>> appropriate tag, like e.g. usage=* (please ignore if the specific tags I
>> put in the examples are not of your liking: not the point here, let's
>> discuss that later...).
>> >>>>
>> >>>> Arbitrarily overloading words with meanings they do not have in the
>> common language is just a perfect way to Babel, that is a reduction in
>> information.
>> >>> + 1
>> >>>
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