[Tagging] RENDER

[Peter Wendorff]

Okay, let me get a bit more verbose.

I want to get Walmarts shown on the map in a different color.
Before there's a polygon with the following tags:

shop=supermarket
building=yes
operator=WalMart
addr:street=whatever
addr:housenumber:42
addr:city=YouLike
render=blue

Another polygon is tagged

shop=supermarket
building=yes
building:levels=2
operator=WalMart
addr:street=another street
addr:city=some city

Let's consider the usual rendering of the osm-carto (default mapnik)
stylesheet.

without considering the render tag both buildings are drawn as buildings
(dark outlined polygon filled in slightly lighter gray) and a shopping
cart icon on top.

Now let's consider the render-tag.

Variant 1: just use it. You get an entirely inconsistent look, as I
myself wasn't interested in all WalMarts, but probably only those in one
particular town, so I only added the render tag to some objects.
Let two others add arbitrary, but different render ideas to other
objects and the map get's unusable as there's nothing like a map key any
more: all visuals on the map get more or less meaningless.

Variant 2: Try to use the render tag, but in a consistent way.
In that case my stylesheet/renderer would have to figure out what is
meant by the render-tag. It may refer to supermarkets, to WalMarts, to
stuff in the whatever-street or in the city YouLike. Figuring out a rule
from that is incredibly hard and very error prone.

Your last sentence might be the misunderstanding:
"As soon as rendering is defined for an element, it is used instead and
RENDER is normally ignored".
But even that is a tricky strategy. Let's stay at the WalMart-Example.
I want to have a special (!) rendering for WalMarts, so there is no
rendering defined for it before (as any rendering defined is a fallback
to a more generic case: supermarkets or even buildings).
It would therefore lead to cluttering map objects where it is not
necessary, or doesn't solve anything at all. Although it would break
down stylesheet innovation even more as you can render your very own
tags - as long as it isn't rendered on the map itself.

Put the effort to add rendering for missing objects. This is harder to
achieve, yes; but it is the straightforward way, not a hack around, with
major drawbacks and side effects.

regards
Peter

Am 20.08.2014 um 14:46 schrieb André Pirard:
> On 2014-08-15 16:31, Peter Wendorff wrote :
>> not a good idea IMHO.
>> 1) what is the feature this tag should refer to? Consider a polygon that
>> is tagged as a building (building=yes) and a shop (shop=supermarked) and
>> a Walmart (operator=WalMart), and the mapper added RENDER=blue. What is
>> it that should be rendered blue? This object? Any supermarket? any
>> Walmart? 
> I don't understand what you say very well. "added RENDER" to what?
> As I say RENDER would typically apply to "an area", to one object, not
> to "any".
> That is, you have building=yes + render=blue and that building gets blue.
> 
>> Any building? How should any rendering decide if the default
>> rendering should be used or the one defined by the tag you propose?
> Did you read my sentence:
>>> As soon as rendering is defined for an element, it is used instead
>>> and RENDER is normally ignored.
> ?
> a.s.o. ...
> 
> André.
> 
> 
>> 2) I want to get Walmarts shown on the map in a different color, thus
>> all Walmarts I want to see in the map get
>> RENDER={mycolor-which-is-not-used-yet-in-the-zoomlevel-I'm-interested-in}.
>> Now the stylesheet maintainer uses that color for another object -
>> conflict, damn, fail.
>> 3) I want to get Walmarts rendered pink on osm-carto, green on HOT,
>> orange on the cyclemap - what should go to the render-tag (even if the
>> styles would follow your proposal?
>>
>> The only benefit I see in this proposal is just what you said: people
>> would stop tagging stuff just to get their map to display it the way
>> they want; but how do you ensure they don't tag stuff to be rendered
>> with the same style? How do you ensure the map stays usable?
>>
>> regards
>> Peter
>>
>> Am 15.08.2014 um 16:12 schrieb André Pirard:
>>> Hi,
>>>
>>> It's a well known fact that many people complain to tag in vain because
>>> what they tag doesn't show on the map (e.g. mini-golf vs tennis pitch),
>>> because they're told to open a rendering ticket which replies that only
>>> official tags are supported, and because they open a vote for an
>>> official tag and nobody signs.
>>> As a result they are accused of "tagging for the renderer" instead of
>>> 'being forced to tag for the renderer".
>>>
>>> The solution is simple however.  A RENDER tag that, typically, would
>>> assign a color to an area.
>>> I'll let the rendering specialists define what else it can do.
>>> ⚠ ⚠ ⚠ RENDER only requests *by default* rendering.
>>> As soon as rendering is defined for an element, it is used instead and
>>> RENDER is normally ignored.
>>>
>>> For a better map,
>>>
>>> André.
>>>
> 
> 
> 
> 
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