[Tagging] exit_to on motorway_junction

Paul Williams pjwderby at googlemail.com
Wed Nov 21 00:21:09 GMT 2012


Hi Johan,
I don't know about storing information for a router, I'm just speaking 
from the perspective of myself as a mapper and saying that to me exit_to 
on a junction node seems a simple and established way of recording exit 
destination signs, so I don't see why I and other mappers using exit_to 
should change from this. On a simple short one way motorway slip road 
with just one road leading on to it, as in your example, I can see that 
destination tagged on the way probably wouldn't be a problem. However on 
longer and more complex ways you'd need to make sure that the roads were 
split before every junction - to identify the point where the 
destination is signed, as the destination(s) could change at different 
points along that road.

Cheers,
Paul


On 20/11/12 23:02, Johan C wrote:
> Well Paul, the fundamental question is: where do you store the 
> information needed for any router, in a node, in a way or in both? In 
> my opinion destination on a way can work very well, please take a look 
> at this example:
>
> http://wiki.openstreetmap.org/wiki/User:It's_so_funny 
> <http://wiki.openstreetmap.org/wiki/User:It%27s_so_funny>
>
> Cheers, Johan
>
> ps no destination relation needed in this example, which makes it more 
> compliant to KISS
>
> 2012/11/20 Paul Williams <pjwderby at googlemail.com 
> <mailto:pjwderby at googlemail.com>>
>
>     I don't see any reason to deprecate exit_to, it seems to be the
>     simplest method of mapping a destination sign on a motorway
>     junction or similar exit. I use exit_to fairly frequently and it
>     has been a documented tag for a while (although on the motorway
>     junction page rather than it's own page) and is also used in JOSM
>     presets.
>
>     I feel it is a less ambiguous tag than destination (as a tag on a
>     way) as it shows the specific point where a destination is signed,
>     unlike destination tagged on a way. If you use destination as a
>     tag on a way then I think you'd need to be sure that at every
>     point along that way the destination(s) given is the same
>     throughout and if not or you didn't know you'd need to split the
>     way. The Taginfo stats also seem to show that exit_to is the most
>     popular of the three different ways of mapping destinations: a
>     destination relation, exit_to on a junction node, or destination
>     as a tag on a way.
>
>     A destination relation is also a clear way of mapping a
>     destination as the intersection and both the 'from' and 'to' ways
>     are part of the relation, and is particularly useful in mapping
>     situations where exit_to wouldn't work (like at a crossroads) so I
>     do also use this method. It is however more complex (and so is
>     unlikely to be a method that a new mapper would be able to use)
>     particularly where there are multiple destinations given on a sign
>     which requires a relation for each destination.
>
>     Cheers,
>     Paul Williams
>     (Paul The Archivist)
>
>
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