[OSM-talk] Divided roads proposal

Richard Mann richard.mann.westoxford at googlemail.com
Fri Dec 4 13:11:09 GMT 2009


+1 (on tagging vs drawing models)

I think it's a good rule of thumb that if it can't be rendered easily, then
you need to look again at your tagging model - your data isn't structured in
a way that is usable

Never tag for a renderer. Always tag for the renderers.

Richard

On Fri, Dec 4, 2009 at 9:35 AM, Morten Kjeldgaard <mok at bioxray.dk> wrote:

> This discussion is reminiscent of other discussions just like it.
>
> There are two orthogonal approaches to mapping in the OSM. One is the
> "drawing" approach, which is the most intuitive, since it reminds of
> the way maps have been drawn with paper and pencil for hundreds of
> years. The drawing approach is favoured by newbies and people who
> mostly care about having a beautiful, detailed map to look at. The
> other approach is the "tagging" appoach, where details about the
> landscape are mapped onto a line passing through it.
>
> The "tagging" approach to mapping puts emphasis on a graph
> representation of the surrounding world which for example can be used
> for routing, area- and distance determination, and may types of
> statistical and database applications, situations where the "drawing
> method" doesn't work. Therefore, the "tagging" method has some digital
> properties that are incridibly useful and powerful, and it is these
> properties that is the innovative secret behind the incredible success
> of OSM.
>
> The regrettable fact is that more and more mappers don't realize the
> incredible power of the tagging approach. Drawing dual carriage roads
> as two separate ways is appealing in many ways since "that's how it
> looks". However, it creates problems in more complicated situations,
> for example if intersections with other roads, with cycle- and
> pedenstrian paths are involved, because the connectivity very easily
> gets screwed up. Keeping the connectivity correct forces you to draw
> things that aren't representitive of the real world, and suddenly, the
> drawing isn't "pretty". The result is, such as I've seen lately, that
> people start to say "why should we care about routing at all?"
>
> One example:  an intersection of  two crossing dual carriageways will
> result in four nodes. If the intersection is regulated by a traffc
> light, you will need to specify four traffic lights, but to OSM this
> will appear as four intersections, and passing through the
> intersection, your GPS will think you have to pass two intersections
> instead of one. So, here, while drawing dual carriageways as two ways
> "looks right", it is wrong from a topological point of view.
>
> There's nothing you can do with drawing that can't be done with
> tagging, and there's in principle nothing being done with tagging that
> can't be rendered beautifully on the final map. It only depends on the
> richness of the tagging language and the sophistication of the
> renderers.
>
> It is very important that OSM keeps its head straight and doesn't
> succumb to the increasing pressure of making the map a 2D-drawing of
> the world.
>
> Cheers,
> Morten
>
>
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