[Tagging] Comparison of tag support: Mapnik, Osmarender, Potlatch, JOSM, Kosmos, Map Features (wiki)

Ulf Lamping ulf.lamping at googlemail.com
Mon Dec 14 09:46:51 GMT 2009

Am 14.12.2009 10:05, schrieb Steve Bennett:
> On Mon, Dec 14, 2009 at 12:23 PM, Ulf Lamping
> <ulf.lamping at googlemail.com>  wrote:
>>> Yeah, and I think there is an unfortunate problem where the
>>> wiki/mappers don't want to tell the renderers what to do, and the
>>> renderers don't want to tell the mappers how to map.
>> And I guess this is a good thing.
> I think it would be even better for the mappers to give guidance to
> the renderers, like "This tag should be rendered distinctly from that
> tag" or "the combination of x,y,z should be rendered identically to
> tag w".

The mappers very often can't find a consensus how to tag stuff. In the 
end this would probably mean that lot's of mappers annoy a very limited 
amount of rule writers ;-)

>> I guess this is also a lack of man power. Don't underestimate the amount
>> of time that is needed here. Having the actual usage numbers from e.g.
>> OSMDoc[1] would really help here.
> Yeah, I was just having a look at tagwatch, which has usage numbers
> for the few hundred tags that are explicitly referred to in the wiki.
> Can't see how to get global numbers though - only by continent. I may
> try and integrate these numbers, but I'm a bit wary of what they mean.
> (eg, one bulk import of 10,000 nodes with a certain tag should not
> necessarily "count" for more than 8,000 nodes created manually by 20
> different mappers.

True. But I'm not sure if this is an often found problem in this case.

BTW: tagwatch has a problem especially with the most used keys, see:


It will stop adding new values to the key list, if there are 300 items 
already accounted (IIRC due to memory reasons). So these numbers has to 
be taken with caution.

>>> It might be better to think in terms of "core" tags and "specialist"
>>> tags or something. If something is core, we expect all decent
>>> renderers to render it.
>> How do you enforce this with people doing the renderer maintenance in
>> their spare time? ;-)
> I didn't say enforce! All I'm saying, is you give a list of
> priorities, like "all renderers should support these tags". Just like
> when you "saw what the other renderers are doing", I think programmers
> would be inspired to implement that kind of list. And obviously
> certain kinds of tags can be implemented very easily, just with a
> colour or whatever, while others are harder.

With all the stuff we already have, nothing is "very easy" to implement 
as adding new stuff will make it harder to read the existing stuff on 
the map :-)

Maybe a "top hundred" of mostly used, but not rendered tags would be 
nice. I've started something similiar some time ago, but you'll have to 
somehow filter out tags that won't be interesting, e.g. created_by will 
be very often used but usually not rendered on a street map (although 
osmarender once rendered it). I guess, this filter will look quite 
different for the different renderers.

>> I think its a much better way to display each renderer maintainer: Look,
>> these are the tags that x, y and z are rendering and you don't. Maybe
>> you've just missed it? And also the other way round: No one else is
>> rendering x=y, maybe this is a bug?
> Yep. And the one I'm concerned about, "renderer X supports tag A,
> renderer Y supports tag B, yet A is pretty similar to B". The mass of
> landuse=* and natural=* are pretty haphazard - I don't think any sharp
> distinctions are being recorded.

Maybe as a first step we'll iron out the unintended differences between 
the renderers. That would already be a huge success! If this is done 
(and this will take some time and effort) then look at the missing 

>> As mentioned already, the next best step IMHO would be to have the
>> actual usage numbers from OSMDoc.
>> However, it's up to you what you do with your free time :-)
> Doesn't mean I don't want suggestions!
>> [1] http://osmdoc.com/de/tag/sport/
> Is there a way to get a big dump from this? I can only see a way to
> access one key at a time.
> Fascinating stuff, though. I note the usage of
> "leisure=nature_reserve", "natural_reserve" and "nature_preserve".
> Also, 457 leisure=swimming_pool, but 7188 sport=swimming.

Hint: Don't try to get it all right in one rush, it will only make you 
mad ;-)

If you look at OSMdoc or tagwatch, you'll find a *lot* of stuff that 
won't make sense (at least when you first look at it) and you'll find 
lot's and lot's of typos.

Regards, ULFL

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