[Tagging] Formally informal sidewalks

Nick Bolten nbolten at gmail.com
Fri Jul 14 14:32:20 UTC 2017


> --> need to add all driveways?

This is generally a good idea - and to make sure they share a node.

> --> need to draw virtual crossings at junctions?

These aren't totally artificial/virtual. You can consider them 'unmarked
crossings' and there's already tags on the wiki: highway=footway,
footway=crossing, crossing=unmarked.

Most, but not all, 'weird' routes can be avoided by adding unmarked
crossings. One exception is routing between two POIs on opposite sides of
the street, but:
  - This is not a primary use case for end user routing. If foot traffic
can reasonably be expected to cross anywhere and it's just across the
street, the end user can figure out their actual path easily. Users that
aren't comfortable figuring out that path should most likely not be
crossing at arbitrary locations, and would prefer crossing at junctions
(and preferably marked crossings).
  - Routers can always fall back to using streets / ignoring footways for
short distances. Routers that bake costs into their graph will need to
create an extra graph, but that's an inherent limitation for extending that
approach.

> Throwing out the R word here - what about a relation that defines
> which disconnected ways could be walked to or across from any point on a
> current way?   That would also include the road since there would be no
> barrier.

This is potentially tricky and should probably go in its own thread
eventually (OpenSidewalks people and I have been meaning to do a good
overview and RFC related to it). Example:

- The left side of the street has 1 sidewalk line (sidewalk A)
- The right side of the street has 2 sidewalk lines (sidewalks B, C), split
right in the middle of the block

Drawing:

AAAAAAAAAAAAAAAAAAAA
---------------------------------------
BBBBBBBBBCCCCCCCCCC

I think this would imply needing 2 relations. And if the relation only
contains the info 'sidewalk A', 'sidewalk B', 'street', the simple
interpretation implies that one can always get from sidewalk A to sidewalk
B via the street. However, not all crossings from A to B are orthogonal:
the diagonal crossings may be impractical. So routers will need to
incorporate spatial logic as well, essentially just adding unmarked
crossings at various points. Totally doable, but not super simple, either,
and that strategy doesn't actually require the relation.e

A natural reaction is to revert to treating sidewalks as metadata of
streets, but this is no good for accessible routing, and is also not a good
description of the pedestrian transportation network. But for the most
part, I have yet to see an example of a really bad route when unmarked
crossings are added at appropriate locations.

On Fri, Jul 14, 2017 at 6:50 AM Marc Gemis <marc.gemis at gmail.com> wrote:

> Another typical case
>
> - no explicitly marked crossings
> - sidewalk parallel to road
> - kerb separating sidewalk from road
> - hedge, interrupted for each driveway and at the junctions, placed on
> sidewalk, parallel with road.
>
> --> need to add all driveways ?
> --> need to draw virtual crossings at junctions ?
>
> m
>
>
> On Fri, Jul 14, 2017 at 3:41 PM, Mike N <niceman at att.net> wrote:
> > On 7/14/2017 8:14 AM, Marc Gemis wrote:
> >>>
> >>> but merge sidewalk with the road where the is no space/barier between
> >>> them.
> >
> >
> >> and that's were the discussion starts. When I asked when one has to
> >> draw a separate sidewalk a few weeks ago on this mailing list someone
> >> answered: as soon as there is a kerb.
> >
> >
> >   Similarly, I have been combining sidewalks with roads where there is no
> > separation.   But when there is a small grass separation from the
> roadway,
> > they are drawn separately.  For those cases, it is usually allowed to
> cross
> > the grassy separation and the road to get to the opposite sidewalk.
> >
> >   Throwing out the R word here - what about a relation that defines which
> > disconnected ways could be walked to or across from any point on a
> current
> > way?   That would also include the road since there would be no barrier.
> >
> >
> >
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