[OSM-talk] Divided roads proposal

[Steve Bennett]

(Weird, did this email not get sent before - so many emails going back
and forth. Oops.)


On Fri, Dec 4, 2009 at 4:37 AM, Martin Koppenhoefer
<dieterdreist at gmail.com> wrote:
> no, I think this is a big con: there are (and will always be) people who
> change the map to different schemes, sometimes also loosing information
> (e.g. on talk-de it was recently reported that people delete separately
> mapped cycleways and attach cycleway=track to the road, what is loosing
> information (positional and inhebitance of tagging different maxspeeds,
> surfaces, widths, etc.). If the new way is containing less information,
> don't set it online.

Well, I guess I agree with you, but that's a big "if". And it's a
question of mapping practice, not of software functionality. There are
a few scenarios:

1) There is a divided road that has been carefully mapped out.
Converting this to a simple divided=* tag could lose information.
2) There is a divided road that has been sketched out roughly, simply
to indicate the division. (Very common, I think) Converting this to a
simple divided=* tag doesn't lose information, and better indicates
the actual level of information stored.
3) There is a divided road which is represented as a single road,
because it's not particularly important, or the mapper was lazy or
whatever. This could be a *gain* of information.

As an example of 3), see this randomly chosen spot:
http://www.openstreetmap.org/edit?lat=-37.747252&lon=144.7879&zoom=19

(Turn on nearmap to see the imagery). There's a corner with a brief
division as a safety device. You probably wouldn't map that as two
lanes, because it would look ugly and superfluous. But it would look
elegant with a simple divided=* tag.

Here's one that looks like 2):
http://www.openstreetmap.org/edit?lat=-37.77825&lon=144.830416&zoom=19

There are two lanes to indicate the divided highway, but the mapper
hasn't marked out the cut throughs, so this results in worse mapping
than if they'd just made a single road. - the router can't tell that
you can turn left across the median strip.

If you follow that road south a bit, you'll find cases of 3 and 2:
painted lines, some of which are marked as separate lanes, some
aren't. IMHO it would be cleaner to represent all of those with a
divided=* tag, but tthat's just my opinion.
----

http://www.openstreetmap.org/edit?lat=-37.77888&lon=144.833565&zoom=19

A clear example of 1: obviously you would not convert this massive
median strip into a single way.

http://www.openstreetmap.org/edit?lat=-37.786651&lon=144.84961&zoom=19

Another 1), I think. An interesting shaped median strip best left as two ways.

http://www.openstreetmap.org/edit?lat=-37.785579&lon=144.854427&zoom=19

But just a bit down the road, the median strip is very  uniform. It's
probably wide enough to justify the two lanes, but it's worth asking
the question.

http://www.openstreetmap.org/edit?lat=-37.791938&lon=144.86358&zoom=20

Also worth asking whether a traffic island is different from a short division.

Steve