[Tagging] In defence of OSM Carto (was: Re: Irrigation: ditches, canals and drains)

[Christoph Hormann]

On Friday 31 May 2019, Andy Townsend wrote:
>
> I suspect that the OSM Carto style would be open to pull requests
> that looked at the sub-tags of canals etc. if it could be done in a
> way that wasn't over-complicated - look at OSM Carto's handling of
> leaf type for a possible way forward.

Indeed.  There is discussion on this happening in:

https://github.com/gravitystorm/openstreetmap-carto/issues/3354

The important thing is to look at the data and to do it world wide and 
to avoid wishful thinking along the lines of "this tag looks like it 
could be useful to differentiate rendering so let's just assume is is 
actually used in the a way it would be helpful".

leaf_type is easy because it represents a simple and well defined 
biological fact.  Characterizing canals as human built structures in a 
similarly clear way is much harder.

> A bigger problem is the lack of granularity of rendering width at
> various zoom levels (see for example
> https://www.openstreetmap.org/#map=13/54.1856/-0.8334 ,
> https://www.openstreetmap.org/#map=14/54.1850/-0.8258 and compare
> with
> https://map.atownsend.org.uk/maps/map/map.html#zoom=14&lat=54.18504&l
>on=-0.80956 ).

Yes.  As mentioned in 

https://github.com/gravitystorm/openstreetmap-carto/issues/3354#issuecomment-496449087

the whole waterway line with stepping across zoom levels is full of 
fairly strange historic artefacts and not really well thought through.  
Combined with removing minor waterways from z13 waterways are quite a 
mess now.

And more generally speaking creating a map style that does an equally 
decent job at representing all kinds of geographic settings around the 
world as it is the stated aim of OSM-Carto is inevitably a constant 
uphill battle because the vast majority of mappers and developers in 
OSM simply are from urban environments in Europe and North America 
which brings an inherent bias with it.  How well OSM-Carto manages to 
fulfill its function to create a map for the whole OSM community to a 
large extent depends on how well we manage to compensate for this 
inherent bias.

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