[Tagging] Feature proposal - RFC - Connectivity

Leif Rasmussen 354lbr at gmail.com
Sat Jun 1 02:49:24 UTC 2019

https://www.openstreetmap.org/#map=19/38.94280/-77.25527marc marc wrote:
> in the rational, you said "there are many cases where turn:lanes=*
> can't provide that information."
> could you add a case where turn:lanes are included that more
> clearly shows what the connectivity=* adds ?
> ideally 2 examples that would have the same turn:lanes value for the
> "from" way and the same number of lanes on the "to" way but not the
> same connectivity=* value

That was the original rationale, but as the proposal improved, I saw a much
greater potential in these relations, which I have now documented in the
There are still some cases where turn:lanes can't properly mark the
connectivity of the intersection without the mapper going out of their way
to make the intersection compatible.  Most intersections are technically
possible to map, but connectivity relations will make it cleaner and
simpler to do so.

* The main usage of this proposed relation will be to state which lanes
connect to which when the number of lanes on a motorway changes.
* The second most important usage of connectivity relations will be to
document actual lane connectivity where lane markings don't actually
represent reality - for example, a left turn lane might be able to turn
left on to a residential road, but also continue straight to another left
turn lane which turns left that the next intersection 100 m away.
* The third usage is for representing a few complex intersections where
lane mapping gets complicated.  It is almost always possible to mark *node*
intersections with turn:lanes, but when things get confusing (like
https://www.osm.org/#map=19/38.94280/-77.25527), it's not always obvious
what counts as what.

There are likely many other places where it will be nice to have this tool
for clarifying lane connectivity that I haven't heard of, since I'm always
discovering more.

So, to sum up the rationale, this proposal adds a whole new level of detail
to osm lane data that will allow for new usage possibilities including
better lane centered navigation.

Thanks for the comments!
Leif Rasmussen
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