[Tagging] Mapping nonexistent paths

[Sinus Pi]

Take a large plaza with, say, six different streets entering. In practice,
the whole area is open for pedestrians, so they'll cross it however they
please, probably taking the shortest routes between streets. What choices
are there to make a router's job easier?
- Draw a "spider" of streets, connecting at the center of the plaza:
easiest for routers, horrible for renders.
- Rely on the plaza shape to be routable: line-of-sight optimization is
supported by some routers, so the dreaded around-the-perimeter routing
isn't the only way, but it could take ages for routers to adopt a proper
algorithm.
- Draw virtual highways: easiest for routers, but now the renders would
have to know not to draw them.

As for Bert's approach, that ALL highways are essentially virtual the way
we use them - it's one thing to draw a line along a street, resembling it
in real world pretty accurately, and another to draw a virtual river across
a lake or a canal across a sea, resembling a route that doesn't physically
exist at all.


On Tue, 23 Mar 2021 at 11:37, Bert -Araali- Van Opstal <
bert.araali.afritastic at gmail.com> wrote:

> I am sorry but I am still not seeing the advantage or added value to
> introduce keys or values to indicate that something is "less visible" or
> "less verifiable" or virtual or whatever you call it. I can't fit it in the
> model that exists in my mind how we map things, especially ways in OSM.
>
> All highways, all their connections, all rivers are virtual in OSM, all
> routes are virtual.  We map them by drawing and connecting ways across
> surfaces.  A pavement that stops "early" doesn't mean the path, the route
> people walk stops there.  That is insufficient completeness in the mapping.
> Every highway or lane is mapped with a "virtual" line in the middle, the
> "virtual" route people or vehicles follow across a surface, be it asphalt
> grass or whatever.
> Ferries and boats move across a lake on "virtual" routes, they just follow
> a path on the water surface, in many cases not aligned by buoys or other
> means.
> The same for coastlines, the "virtual" coastline is where the median is
> between the salt and fresh water.  In cartography many times just a
> straight line.  You want to indicate the river connects to the water body
> and which route boats or ships follow, you map it, with our present
> complete "virtual" waterway schemes.
> I still have to see the first example where that doesn't apply or is not
> described nicely in our wiki.
>
> What does adding an additional tag add to this concept ? Makes it more
> complex to the mapper, because he has to add a tag for something considered
> more virtual in an already virtual scheme ? What is the added value for the
> mapper, I see none.
> What is the added value for the router ?  I can't imagine even one?  Do
> you think routers will evaluate the virtual tag, no they just look at the
> ways, the routes in general that are already there.  Knowing that it is
> perceived as more virtual by some has no added value for the router.
> For the renderer, other data users ? Any added value for a virtual or
> invisible tag in comparison with what we already have ? I can't find any.
> Please show me an example where the current tagging would be considered
> less favourable to be used as is ?
>
> So, thank you for making this proposal, you made some nice examples which
> we could maybe add to the highway page.  But it's just examples how OSM
> provides a bright and consistent way to map complex realities and
> behaviour, AS IS. It works, use it as intended, don't make it more complex
> by adding tags without added value.
>
> Greetings,
>
> Bert Araali
> On 23/03/2021 12:38, Martin Koppenhoefer wrote:
>
> sent from a phone
>
>
> On 23 Mar 2021, at 10:23, Niels Elgaard Larsen <elgaard at agol.dk> <elgaard at agol.dk> wrote:
>
> Can anyone give an example of such a sophisticated router available to OSM users?
>
> the routers don’t have to be sophisticated if you connect highways to polygon highways, it’s sufficient for most cases to route around the borders (will be a little bit longer, but mostly not have practical consequences for the suggested route)
>
>
> Cheers Martin
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