[Tagging] The endless debate about "landcover" as a top-level tag (was: Re: British term for municipal greenery?)

Andy Townsend ajt1047 at gmail.com
Wed Jun 6 12:37:00 UTC 2018


On 06/06/2018 11:48, Peter Elderson wrote:
> This issue has a long history... seems to me tagging awaits rendering, 
> and rendering awaits tagging. In such cases, you need a commitment 
> from both sides, with enough support to fuel trust. Then things can 
> get rolling.

Speaking as someone who both adds things to the map and maintains a map 
style, only the second of those is really true - rendering does 
(thankfully) follow tagging, rather than whatever someone happens to 
have changed a wiki page to recently.  Tagging absolutely _does not_ 
follow rendering - as I've found out many times when looking through 
taginfo.  Very often someone wants to say "here's this thing that's 
important to record, but OSM doesn't really have a concept for it yet".  
When people wanting to record the same thing search taginfo the "new 
tag" gains acceptance and when that happens renderers start to take 
notice.  Lots of what this* map renders was found by looking to see what 
values people actually use for keys (see e.g. much of what is in 
here**).  Many of the tags that people use aren't rendered anywhere 
(think of address detail) but they're still really useful to add.

The problem with e.g. landcover=grass is that it's recording _exactly 
the same information_ as a more widely used tag conbination 
(landuse=grass).  You might argue that landuse=grass _should_ mean 
something different, but as used in OSM right now it just says "there is 
some grass here".  That's the one of the reasons why the OSM's "standard 
style" doesn't render it - the "feedback" bit of 
https://github.com/gravitystorm/openstreetmap-carto/blob/master/CARTOGRAPHY.md 
has been changed recently, but the style always intended to focus on the 
"normal" way to express a particular concept (you wouldn't invent a tag 
"highway=my_special_road" for an existing concept, you'd pick the best 
value in common use and use other tags to indicate what makes your road 
different).  The wiki page 
https://wiki.openstreetmap.org/wiki/Tag:landuse%3Dgrass says "It is 
typical that landuse 
<https://wiki.openstreetmap.org/wiki/Key:landuse>=grass is misused and 
should be changed to landcover 
<https://wiki.openstreetmap.org/wiki/Key:landcover>=grass 
<https://wiki.openstreetmap.org/wiki/Tag:landcover%3Dgrass> ".  I'd 
argue that that's wrong; it's the majority usage of a tag by thousands 
of people that determines what is "correct", not a wiki page edited by 1 
or 2.

In the case of the use of "landcover" as a top-level tag, at least in 
the areas that I'm interested in rendering, landcover really hasn't 
troubled the scorers (see 
http://taginfo.openstreetmap.org.uk/tags/landcover=grass as compared to
http://taginfo.openstreetmap.org.uk/tags/landuse=grass ).   I've 
actually added support in my style at 
https://github.com/SomeoneElseOSM/SomeoneElse-style/blob/master/style.lua#L1076 
because I'm not worried about providing feedback in the way that the OSM 
Carto style is, but it's only in there as a little-used synonym for a 
concept in OSM that most people express a different way.

The tagging list does occasionally fall into the wiki-hole of trying to 
tell people how to map rather than communally deciding the best way to 
map something (including by looking at how people already do).  In any 
situation where you're trying to suggest that "everybody else is wrong" 
you need to get over it, and OSM in particular has thrived where other 
similar projects failed simply because people can always find a way of 
expressing a particular concept - they can create a way of representing 
it themselves without a "domain expert" creating it for them first.  
There may well be a concept out there waiting to be mapped that needs a 
"landcover" tag (and it might be "municipal greenery"), but it's not 
grass or trees.

Best Regards,

Andy


* https://map.atownsend.org.uk/maps/map/map.html
** https://github.com/SomeoneElseOSM/SomeoneElse-style/blob/master/style.lua

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