[OSM-talk] Highways tagging vs Polygon

[Lauri Kytömaa]

Radomir Cernoch wrote:
>> http://openstreetmap.org/?lat=60.18933&lon=24.9642&zoom=18
>I do not
>think that streets like Sturenkatu or Teollisuuskatu, nor any of
>connected primary/secondary/tertiary form a "zone". I would suggest to
>define a "zone" as an "area with predominantly uniform traffic
>regulations".

Not that it matters in Finland, but urban roads are more often signposted
as "zone 30" or "zone 40" and not "maxspeed 30/40", at least in Helsinki.
Such zones can't be made up at will, but can only be surveyed by entering
an area from all directions. To me the maxspeed is just a property of the
road, even if the authorities have signed them as a maxspeed zone.

Likewise the urban area (as defining the applying traffic rules, mainly 
maxspeed=50/80) can't be accurately deduced from landuse areas, 
residential roads nor from any administrative boundaries yet entered. The 
only relevant legislative differences are the maxspeed and whether honking 
is allowed to signal starting an overtake, but no one does that anyway.

Examples:
in http://openstreetmap.org/?lat=60.221&lon=25.035&zoom=16
everything is urban, but
in http://openstreetmap.org/?lat=60.193&lon=25.03&zoom=16
only the trunk road is not urban (as are all trunk roads inside Helsinki)

>* 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).

Actually, if there was a polygon with zone:traffic, it'd likely be wrong.
Those roads most likely have a maxspeed of 30 or 40 and without a proper
survey(*1) they would still be inside a zone:traffic=urban, which would
imply a maxspeed 50 in Finland. Guessing a zone from the other minor
roads, roads that aren't connected to those without a maxspeed
(Allotriankuja and Rialtonkuja in the example), would indicate a maxspeed
zone of 30 or 40 - a 50 percent probability of being wrong. Without a
given maxspeed it's known to contain incomplete information.

*1 Someone unkown drew most of the roads in Helsinki in 2007 from the
Yahoo aerials and there's still much to add details to. A chance to get
the house numbers, too. It's a work in progress, even if it looks quite
detailed in places.

With about 600 mappers (ever having edited anything) in Finland and 300 
000 km of roads it's going to take a whole lot of time, esp. outside the 
significant cities.

-- 
Alv