[Talk-GB] Tagging of British canals.

[SK53]

Hi Richard,

The basic problem is that the wiki descriptions tend to be prescriptive
(and written by people who do not map very much themselves) rather than
descriptive. For this reason many (perhaps most) mappers in Great Britain
tend not to place great reliance on wiki definitions. I was certainly
unaware of this tag usage, although it appears to have been applied locally
<http://www.openstreetmap.org/way/77921444/history>several years ago.

Whatever its faults waterway=riverbank has been the standard way to show
the areal extent of canals as well as rivers by UK mappers. To date there
appear to be 1674 polygons <http://overpass-turbo.eu/s/4tA> with
natural=water + water=canal of which 1541 have you as their last editor
<http://overpass-turbo.eu/s/4tx> . Of the latter only one seems to retain a
waterway=riverbank <http://overpass-turbo.eu/s/4ty> tag. No doubt an
oversight on your part.

Although you may have mapped these in the first place lots of other people
have looked at them and found the original tagging acceptable. I certainly
did when adding detail along the eastern end of the T&M 3 years ago. So a
tagging consensus arises not just through how people map things, but also
through people accepting a given way of tagging and therefore *not touching*
things when mapping close by.

I was vaguely aware of your edits but hadn't looked at any in detail.
Broadly speaking I would say adding the natural=water + water=canal is
probably fine, but deleting the waterway=riverbank is not. Large scale
changing of any tag on a country wide basis should always be accompanied by
a message to this list (we have recently had a mass change of Marks &
Spencer to Marks and Spencer, and in the past people have corrected "The
Co-operative", which is what is shown on the signs to "Co-op", and so on).
Mass edits tend to give a spurious sense of consensus. It's much better to
get a true consensus : even if the consensus is "agree to disagree".

One other point is that as a consumer of the data you may find this tag
combo works particularly well for your use-case, but it is important to be
aware that the same data may be being used elsewhere and changing the tags
may cause other data consumers not to work anymore.

Personally I'd prefer that we denoted water areas with natural=water and
then waterway=riverbank could be used for linear features and it would be
possible to have nice casings on water bodies in mapnik generated
renderings. However this is not the case and I live with it because its
only a minor annoyance. One problem I notice is that there are a small
number of linear features tagged natural=water+water=canal : I can predict
that someone will advocate on the wiki that this is the only correct way to
tag canals.

Changing how something is tagged usually requires that the new or
alternative way has some compelling advantages over the old way: the
designation tag for rights of way and changing from highway=ford to
ford=yes are two examples I can think of, but the 'new' public transport
scheme has not displaced highway=bus_stop, probably because it was more
complicated and less obvious.

Regards,

Jerry


On 6 August 2014 19:17, richard <richardwest at leiston.info> wrote:

> Firstly a disclaimer, I am mostly an armchair mapper.
>
> I am working my way around the canals of Britain, tracing the canal banks
> and
> tidying up locks etc. (I have probably seen a dozen different ways that
> locks
> have been tagged.)
>
> I started off tagging the canal banks as
>
> waterway=canal+area=yes
>
> but it was pointed out to me by another mapper that this was confusing
> renderers and was pointed to the Wiki entry that suggested they should be
> tagged as
>
> natural=water+water=canal
>
> I therefore changed my existing tagging to reflect this and tagged my
> subsequent tracing this way. I have come across a few areas that have been
> traced by others (Mostly a long time ago and IMHO very poorly) that have
> been
> tagged as
>
> waterway=riverbank
>
> and I have changed these as I have realigned them.
>
> Today I have had a critical message from another mapper who said among
> other
> things,
>
>
> "Wide-ranging changes to existing tagging schemes, just because you read a
> Wiki page is not good enough."
>
> I have two problems with this sentence,
>
> 1/ My CHANGES have not been what I would consider wide ranging as most of
> the
> mapping has been done by myself therefore new not changed.
>
> 2/ If the reading of a Wiki page is not good enough then why bother having
> a
> wiki? Do we have to resort to the mailing list every time we want to tag
> something?
>
> If there is an "accepted" way to map canals can someone point me to it?
>
>
> --
> Richard.
>
>
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