[Tagging] Mismatched Level of Detail in highways vs. other elements

Clay Smalley claysmalley at gmail.com
Sun Apr 7 19:13:03 UTC 2013


I do some mapping in SF too. The Muni Metro lines weirded me out when I
first saw it, and I looked up the proper practice on the wiki as well as
looking for a few examples in Europe, and it seems that the best practice
is to just add railway tags and the proper relations to the street whenever
it runs along a street, and as a way by itself when it runs in its own
right-of-way (such as the J line's jog around a hill a little south of
Dolores Park).

I'd support mapping the Muni Metro lines the European/more common way, if
nobody else has any objections.
On Apr 7, 2013 1:38 PM, "Martin Atkins" <mart at degeneration.co.uk> wrote:

>
> Hi all,
>
> I do mapping in San Francisco, CA and I'm frustrated about the
> inconsistent levels of detail we typically use when mapping urban
> environments.
>
> For example, most highways are mapped in a network-oriented fashion with
> one string of ways representing both directions of traffic, often
> encapsulating other features like cycle lanes and sidewalks, and
> intersections simply represented by crossing the streets at a single common
> node.
>
> On the other hand, rail lines are most commonly mapped by their physical
> shape, so the rail ways come in pairs. The people who mapped the tram lines
> in San Francisco also mapped the curves of the rails at intersections,
> rather than having them meet at a single node as with the highways. This
> creates the following ridiculous effect in rendering:
>     http://osm.org/go/TZHvFT5aF--
>
> Notice how the rails only just fit inside the rendered street on straight
> sections, and cut the street corner completely at the intersection.
>
> However, here's how it actually looks on the ground (looking across the
> intersection from east to west). Notice that the rails are completely
> contained within this 4-lane intersection (all four being normal traffic
> lanes with no physical separation except for the tram boarding platforms):
>     http://oi45.tinypic.com/**w6qsgh.jpg<http://oi45.tinypic.com/w6qsgh.jpg>
>
> (On the plus side, we're doing better than Google Maps, whose rendering
> makes it look like the rails on Church street are both off to the west side
> of the street! http://tinyurl.com/cedot4n )
>
> This problem shows up in various other contexts too: it's impossible to
> accurately tag a bench or bus stop on a sidewalk because the sidewalk
> doesn't exist as a separate construct. Fences or buildings directly abut
> the street end up rendering either over the street or set back from it
> because the true width of the street is not represented.
>
> For most normal street mapping and vehicle routing purposes it seems
> sufficient to just know simple landmark details that aid in orientation,
> e.g. that whether particular street contains a railway or it passes
> alongside a railway. Of course, more detail-oriented uses like 3D
> renderings it'd be more important to have the full physical street layout
> described, with separated lanes and proper physical relationships with
> surrounding objects.
>
> How have others resolved this fundamental conflict? More detailed streets,
> or less-detailed everything else?
>
>
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