[Tagging] Reviving the conditions debate

Tobias Knerr osm at tobias-knerr.de
Wed Jun 13 16:05:34 BST 2012

On 13.06.2012 16:12, Martin Vonwald wrote:
> If you use a different character (like the ? in the 1.5)
> it would be clear where the conditions start.

That's a valid argument, but we need to be aware that there is already a
lot of existing tagging that uses a colon as the condition separator.
These are usually examples with just a single condition, things like
maxspeed:wet, :hgv, :forward, :backward, ...

I also doubt whether the distinction between a "subkey" and a
"condition" would always be obvious to mappers.

> Didn't know about that too. And it has the same problem:
>   maxspeed:lanes:hgv:wet=60|50|40
> Where does the condition begin? Again this is not obvious. Small change:
>   maxspeed:lanes?hgv:wet=60|50|40

That's interesting, I would have assumed that the tag should look like
maxspeed:hgv:wet:lanes to allow for per-lane fallbacks.

For example, if there is only one lane that changes maxspeed when wet,
one might want to write that as follows:

maxspeed:lanes = 80|80|80
maxspeed:lanes?wet = ||50

Yes, you could evaluate this without any knowledge about the semantics
of the base key. But doing so would result in "the value of
'maxspeed:lanes' is '||50' when the road is wet". That's not actually
what we want - we do want the keep the '80' for the first two lanes.


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