[OSM-talk] zones for motorway/in town/outof town?

Radomir Cernoch radomir.cernoch at gmail.com
Wed May 20 22:57:52 BST 2009


Florian Lohoff píše v St 20. 05. 2009 v 23:29 +0200:
> On Wed, May 20, 2009 at 09:05:45PM +0100, Radomir Cernoch wrote:
> > By "traffic zone" you mean a tag "zone=XXX" on each individual road in
> > the city? I'm afraid that such system is very prone to forgotten tags.
> > 
> > If you use a polygon around a city, you can also derive the source of
> > the speed limit. Rules 1) - 3)  mean that being "on highway"/"in
> > city"/"outside city" is the main limitation. Applying rule 4) means
> > there is a physical sign that causes the regulation.
> 
> The problem with the polygon is that in Germany it perfectly possible
> to have streets within the city above the normal city limit
> and also below (very common). So once you put the polygon around the city
> you implicitly bring all streets to city level e.g. 50 although
> there might be loads of streets with 30 kph or 70 kph

Now I get the point. This was discussed in another mail. Of course there
must some way of handling this. We came up with using multipolygon as
the most suitable way of solving this.

> > Yes, in the "polygon" system you would encircle the whole area and every
> > road inside of it has automatically 30 km/h limit.
> 
> Which is IMHO a very dangerous behaviour - i wouldnt want any fact be set
> without checking - so the limit explicitly set on every street is my favourable
> way.
> 
> > Sorry, I maybe didn't make myself clear. "Polygon" rules do not apply
> > for motorways. Is there any country, where a highway inside a city has
> > different speed limit from the highway outside of the city? Even if yes,
> > this can be specified in the set of country-specific rules...
> > 
> > I can imagine a situation, where a normal 50 km/h road goes through the
> > middle of a zone-30. Then there are two options:
> > 1) You split the zone-30 polygon into 2 polygons.
> > 2) You tag the 50 km/h road with "maxspeed=50".
> 
> The problem with the polygon is that you set a default without checking every
> individual street.

Yes, but there are other people as well. What if they add a new street
to the area you have carefully checked and then forget to add the zone
info.

> Id rather check all the individiual streets and tag them
> one by one when i am shure i have the correct fact.

And if JOSM could understand the speed-polygon and told you:
"This road has speed limit 50 km/h because of way 2387567."
Would it be a suitable solution?

> Its not calculating Pi where 3.1 might be acceptable for the start and later
> we calculate more digits. 

Thanks for this formulation. Calculating Pi as 3.1 would be too good in
comparison to the current status of Czech OSM map!

I give you an example of what work I did over the weekend: In CZ most
towns have only basic roads connecting them to neighbouring villages.
So I picked one to create at least the basic road network. I took the
WMS map and database of all address plates, copied them in OSM and drew
residental roads, where they should be. What about speed limit?

1) If I tag all roads as "zone-50", this would be false. I do not know,
that every single road has 50 km/h limit.
2) But I can peacefully draw a "zone-50" polygon around the town,
because I know, where the town has its borders.

When someone more knowledgeable about the town comes after me, he can
easily set 'maxspeed=*' tag to roads, which have such regulation.
If I had put 'zone-50' tag there? What would you do if you find that
someone else had put a tag you consider suspicious? Probably
double-check that place... spending more time checking someone else's
mistake.

Lastly I must say that I really do feel for a perfect, detailed map.
But I try not to forget about other people, especially newbies and also
about those people, who do not spend hours studying wiki.

Radek

> Flo 






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