[OSM-talk] [OSM-dev] Verify upload of trackpoints/segments

[Joerg Ostertag (OSM Munich/Germany)]

On Saturday 21 October 2006 10:18, you wrote:
> On Fri, Oct 20, 2006 at 08:44:08PM +0200, Joerg Ostertag (OSM 
Munich/Germany) wrote:
> > I don't think that the absence of a tag implies a default. I normally
> > first don't tag a segment at all. Then I start tagging with things I'm
> > really sure about. Like foot=yes. If you now happen to have a default for
> > car=yes you always have to tag car=unknown as long until you know which
> > value car= really has.
>
> In other words, you have already chosen a default, your default for all
> tags "unknown" is. So at least we should mention that in the documentation.
>
> Now, secondly, for some tags "unknown" may be a good default. But for
> others I don't agree.
>
> Take your car="yes/no/unknown" example again. What should a user of the
> map do with the information that car="unknown"? Let's say I am writing
> a route planner and the shortest route goes over a segment tagged
> car="unknown". Either I accept the route or I don't. Which boils down
> to either I assume car="yes" or car="no". This means that the tag
> car="unknown" carries no information at all. In practice it will always be
> taken as car="no". So in that case it makes sense to take that value
> as the default from the start.

Well for the routing application you can take car=no as a default, but for 
other users this would be miss leading. I would assume you already checked 
the tagging concerning car=??? and decided it is no. So this would lead me to 
a false conclusion. It tells others that you already know that you cannot 
drive along this segment with a car; which is wrong.

So my understanding was not to tag anything you don't know the status of. 
Maybe sometime later someone else can add this tag with a valid value. So in 
my opinion it really makes sense to leave it like it is: no tag means nothing 
known about this tag.

-
Joerg