[OSM-talk] Cycle lanes

[Dave Stubbs]

On Mon, Mar 31, 2008 at 12:41 PM, David Dean <ddean at ieee.org> wrote:
> Martin Vidner <martin.osm <at> vidner.net> writes:
>
>  > Make the prefixes "left:", "right:" special in the sense that when a
>  > way is reversed, they get swapped.
>  > So left:highway=bus_stop would become right:highway=bus_stop.
>  > (Uh, maybe this is awkward for the renderer implementation. Could be
>  > better to prefix the *value* instead: highway=left:bus_stop?)
>
>
>  It seems to me that you could define the two sides of a way independent of the
>  direction (if any) of the way. I'm just not sure what you would call the two
>  sides.
>
>  For example, lets start with "north" and "south". This would unambiguously
>  define the two sides for all ways that are not running directly (or close to)
>  north-south. "East" and "west" would work for those of course, but we want the
>  same name no matter what the angle of the road.
>
>  Maybe you could use "clockwise" and "anticlockwise" to define the side of that
>  portion of the road you would get if you rotated it in that direction.
>
>  So what I am basically getting at is that you don't need to define the side of
>  the road based on the way direction, as it can be defined by the compass points,
>  I'm just not sure what the two labels would be. Maybe "north-or-east" and
>  "south-or-west" shortened to "noe" and "sow" could work if everything was
>  clearly defined on the wiki.
>

That doesn't work if your way goes round a corner. If I have a way
which forms most of a loop its still ambiguous, and there's plenty
more examples without getting that complicated. For most ways it's
probably possible to pick an arbitrary direction where it's
unambiguous, but you'll never cope with a roundabout, and I think most
people will get very confused anyway, especially as editing the way's
length may change the dominant line direction enough to flip the
meaning.

The only other way I can think of is to stick in a node on the correct
side and link it with a relation that says "this side", but even
that's susceptible to fairly simple editing mistakes.

For proper "mistake proof" editing the only real solution is to use
separate ways. So I'd say just leave direction as significant, but
encourage use of separate ways instead of left/right tags or other
equivalents.

Dave