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

[Radomir Cernoch]

Hi,

your mail suggests it's time for recapitulation.

Firstly let's describe the without-polygon model:

1) Road has tag "maxspeed".
   => I have the answer based purely on "maxspeed" tag.
   => Stop any further reasoning.
2) Road has tag "zone:traffic"
   => I have the answer based on the combination of tags "zone:traffic"
      and "highway".
   => Stop any further reasoning.
3) The answer is "unknown".

Now the proposal of "polygon" model, which emerged through discussion
and which I do support. It removes point 3 and adds:

3) Road lies within a polygon tagged "zone:traffic"
   => I have the answer based on the combination of polygon's tag 
      "zone:traffic" and road's tag "highway".
   => Stop any further reasoning.
4) The answer is "unknown".


Please notice the important point: If we adopt "polygon" model and you
want to use the "without-polygon" model, no problem. It's just enough to
make sure that your road does not lie within any "zone:traffic" polygon.
The freedom is yours.


Ok, then why should we have the polygons?

* It models the law more accurately.
* Therefore you can infer more information.
* You can refine the details of the map gradually over time. At the same
  it allows a truthful interpretation of the OSM data all the time.
* If someone forgets to add the "maxspeed" or "zone:traffic" tag to a
  road, this model is closer to reality. (Please note that this may
  happen in a very well made map, see my previous "Helsinki" mail).
* Therefore it's friendlier to newbies.

The most serious flaw so far:

* The question of querying "node" within a polygon or "line" withing a
  polygon. So far it seems that such query is doable using PostGis.
  Nevertheless this needs to be confirmed.


If you want any details of the points here, please feel free to ask even
if they have probably been posted before. I do not have any other
arguments and unless anyone else does... take it or leave it.

Yours,
Radek Černoch


Mario Salvini píše v Čt 21. 05. 2009 v 14:53 +0200:
> Hi Radek,
> 
> instead of using a complicated polygon-struction (which is btw not as 
> correct as just giving the road a tag) you simple can give any oficial 
> roads (e.g. no tracks oder private service-ways) of the town a 
> trafficzone=in_city and giving the zone-30-roads a maxspeed=30. Finished ;)
> 
> Regards
>  Mario