[Tagging] exit_to on motorway_junction

Colin Smale colin.smale at xs4all.nl
Wed Nov 21 07:37:06 GMT 2012


Using only exit_to there is no way to handle junction topologies other
than a straightforward highway exit, where there is one "big" through road
and one "small" road leaving. What about wrong-side exits? Or where the
highway splits into two (or more) roads of equal importance?

Destination tagging is used a lot in the Netherlands, placed on the first
segment of each way *after* the node where they split. My Garmin warns me
ahead of time which side to keep to, so there doesn't seem to be a need to
start the tagging at the first sign (which may be 1km or more before the
actual junction). I have not yet found a case where adding destination=*
around a junction felt like the wrong thing to do.

IMHO destination=* on the ways is the right balance between the
rudimentary exit_to on the node and using a relation which will have
problems with support/adoption by both mappers and toolmakers.

Colin

> 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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