[OSM-dev] Map files for entire US (for download)

[Al Wold]

It's definitely a little hard to understand the ascii images, especially in
my default proportional font :)  I do see some benefit to separating.  Near
my house, the road is divided in a sort of indecisive manner.  The median is
there at some points, and not at others.  Being able to visualize that on
the map would be nice.  If we had the "superway" object, everything could be
grouped together as being the same road.  If you look at the east-west road
here, you can see the median I'm talking about:

http://maps.google.com/maps?f=q&hl=en&geocode=&q=85048&ie=UTF8&ll=33.30469,-112.045805&spn=0.005425,0.008862&t=k&z=17&om=1

It might be a generally useful idea to have an area on the wiki to post
photos of different road characteristics.  I think it would be particularly
helpful for "outsiders" to understand, since different countries/areas might
not have the same types of road characteristics, traffic control, etc, but
we all have to share the same tagging scheme.

-Al

On 7/27/07, Alex Mauer <hawke at hawkesnest.net> wrote:
>
> Andy Robinson wrote:
> > What's everyone's feelings on this?
> >
>
> My feeling is that separate ways for each direction is quite painful to
> work with in general (especially where two divided roads meet at an
> intersection: the reality is a big square of pavement, while when drawn
> as separate ways there's the effect of an "island" of barrier that's not
> really there.
>
> Places where a road transitions from divided to undivided can also be
> awkward. This is especially so when there's also an intersection at the
> same place.  Crappy ascii art (fixed width font may be required)
>
>       F
>       |
>      D+<--<--<-- C
> A----E+-->-->--> B
>       |
>       G
>
> Lines AE, DC, and EB are all logically the same road (say, "Foo Road").
> Line FDEG is another road, say "Bar Road"
> DE is one way when following CDEA, but not when following GEDF.  I would
> also expect this to be bad for both rendering and routing ("Turn left
> onto Bar road, proceed 1 metre, turn right onto Foo Road")
>
> 5 lane roads, that is, roads with a turning lane ("suicide lane" as
> they're sometimes called.  For clarification, the 5th lane is not to be
> used for normal traffic and passing, only for turning).  These generally
> have a center lane the same width as the divider in a divided highway
> would be (they sometimes transition from divided highway to turning lane
> without angling the road).  They also often have a short (5-10 metres)
> barrier next to any intersections that have a traffic light (for the
> light to stand on, as well as pedestrians crossing).  This means that if
> the 5-lane road is not considered a divided road, you have to divide the
> road just before the intersection, and join it again just after the
> intersection.  Since the lanes go straight rather than being angled,
> there's no good way to make that transition.
>
> Splitting divided roads into two ways does have the advantage of
> simplifying the case where the divider blocks off another road though.
> Crappy ascii art:
>
> A----------------B
> C------F+--------D
>         |
>         E
>
> AB and CFD are one logical road, FE are another.
>
> All these problems just "go away" when divided roads are treated as a
> single way; the last advantage of splitting becomes a simple turn
> restriction.
>
> All these exist within 2 miles of me.  If the ascii art is unclear I can
> provide photos of road sections giving examples.  (some people have
> trouble with the 5-lane road in particular, so I might photograph that
> one anyway to provide an example on the wiki)
>
> -Alex Mauer "hawke"
>
>
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>
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