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

Andy Townsend ajt1047 at gmail.com
Fri May 31 11:13:07 UTC 2019


On 31/05/2019 11:26, Paul Allen wrote:
>
>
> Example of the horrors of using canal for a leat with current carto:
> https://www.openstreetmap.org/way/609805692#map=16/52.0804/-4.6799
> At z=19 it's actually close to the true width of the leat.
>
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.

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&lon=-0.80956 
).

To cut the OSM Carto folks some slack, they're trying to implement a 
global rendering style that has to cope with (in this case) all of the 
different sorts of waterways everywhere on the planet.  There are always 
going to be places where a certain feature is densely mapped and where 
it is important but isn't - look at the way that highway=footway becomes 
essentially invisible at zoom levels where it would be really useful (in 
rural areas) because it would overwhelm the map elsewhere (central 
European cities).  I'm sure that they'd be open to a pull request that 
addressed the stream width issue above, but it'd need to be tested 
elsewhere on the planet - and I'm sure that there are places where the 
presence of a stream is "literally the most important thing on the map" 
at z14.

I therefore wouldn't use OSM Carto as an example of "here's what you get 
when you tag <feature> as X".  Often there's a specialist map somewhere 
designed to show <feature>, and that's probably the better option where 
it exists.

Best Regards,

Andy



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