[OSM-talk] Suggestion: fallback tag

John Smith deltafoxtrot256 at gmail.com
Thu Dec 17 13:00:51 GMT 2009

2009/12/17 Shalabh <shalabh.w at gmail.com>:
> On Thu, Dec 17, 2009 at 6:19 PM, Steve Bennett <stevagewp at gmail.com> wrote:
>> Hi all,
>>   As we all know, you don't "tag for the renderer". However, you want your
>> map data to render nicely now, and you want correct map data in the long
>> term.
>> Suggestion: introduce a "fallback" tag.
>> For example, around my city there are little "reserves" - patches of grass
>> reserved by the government for future development such as freeways or train
>> lines. They often get tagged "leisure=park", but say I want to start tagging
>> them "landuse=reserve" instead. Suddenly, instead of being green on mapnik,
>> it will be white again - unrecognised tag.
>> Solution: tag it like this:
>> landuse=reserve
>> fallback:leisure=park
>> That's pretty simple logic to explain to any renderer or editor, and it
>> gives people a way to avoid the temptation of "tagging for the renderer",
>> and allows them to tag for the future instead.
>> What do people think? (No comments on how to tag land reserves, it's just
>> an example...)
>> (This case is slightly complicated by the fact that the two tags - landuse
>> and leisure - are different. Perhaps a more explicit
>> fallback:landuse=leisure:park would be clearer.)
>> Steve
>> _______________________________________________
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> 1. And what if even the 'fallback tag' is not rendered by the renderer?
> 2. Some things may have just no fallback e.g. Mountain passes are not
> rendered by most renderers. What would be the fallback tag in such a case.
> In my opinion, this will only confuse the mappers more when they tag a POI.
> A few days down the line, we would have many more questions on what should
> be the fallback of what and why?
> I would think a better idea is to have atleast one renderer and the main OSM
> map to render a superset of all tags.


This should be in the rendering logic, not the map data, otherwise
it's no better than tagging things with the icons to use for POIs etc.

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