On 18/08/14 10:59, SomeoneElse wrote:
Whilst the existance of a highway=pedestrian area that isn't connected
is an indication of something, it's usually just an indication of that
mapping in a particular area is not complete.
Considering the longer term problems:
1) There needs to be better guidance to routing software developers on
how to route when there are parallel features accessible on foot;
2) There needs to be a lot more mapping of barriers.
Ideally, the routing rule for foot needs to be something like that,
subject to access and surface quality considerations, if there is no
barrier between adjacent features, you may cross at any point between
them. In this case, there has probably been pressure to make life
easier for the router.
I think this also came up recently with regard to central reservations
on non-motorways.
The other difficult situation we have here is that pedestrian areas are
mapped physically, as the actual area occupied, but most roads are
mapped, abstractly, as an infinitely narrow line on the centre of the
carriageway, so you will get a gap between the two and the router has to
use some heuristics to decide whether that gap is bridgeable on foot. I
have seen cases where the pedestrian area was mapped out to the centre
of the road, but I considered that wrong. (In fact, mapping roads as
areas will generally confuse routing software.)
Another variation of this routing problem is that of where is it
reasonable to cross a road. Ideally, physical barriers at the centre of
the road should be mapped, and access restrictions put on any
reservations that is not supposed to be used by the public, but the main
consideration tends to be the level and speed of traffic and the
visibility of that traffic, combined with whether or not there is a
designated crossing point near enough to be used.
There really isn't enough information mapped to make a decision as to
whether it will be safe to cross. Also, a little old lady may not be
safe crossing at an arbitrary point, whereas it will be no problem for a
more able bodied person. Some people may want to avoid pedestrian
subways, particularly after dark. Any mapping of crime levels in them
is likely to be volatile and may even move the crime.
Particularly for residential roads, you might get into the dangerous
area of mapping actual maximum speeds on rat runs, as, there is a road
near me with a 20mph limit, but, apart from speed bumps it is long and
straight, so vehicles may get up to 40 mph between bumps, with
visibility limited by parked cars. The council policy is to only use
passive enforcement. Mapping that as 40 mph de facto, may encourage
people to use it that way, but saying it is safe for little old ladies
to cross at night, based on the 20 mph limit may also be wrong.
Maybe there is a need for a verification tool that renders additional
random interconnections and crossing points, so that one can see whether
there is a need to add barriers, and other hints, to prevent such routings.
_______________________________________________
Talk-GB mailing list
Talk-GB@openstreetmap.org
https://lists.openstreetmap.org/listinfo/talk-gb
