[Talk-us] proposed first principles for United States road tagging

[McGuire, Matthew]

OK OK. Shot down, shot down (not just by you). I guess since I work for an MPO that classifies roads according to their function, I have a pointy headed definition of function as something that cannot be done by people on the ground, and the results of which are not great for general purpose mapping.

My final thought on the subject is that if the OSM paradigm is "map what's on the ground", I think the combined wisdom of the crowd will bear a dataset that meets your needs by using direct observational classification. Functional classification is indirect and not, "what's on the ground".



-----Original Message-----
From: talk-us-bounces at openstreetmap.org [mailto:talk-us-bounces at openstreetmap.org] On Behalf Of Alan Mintz
Sent: Thursday, March 04, 2010 5:12 PM
To: talk-us at openstreetmap.org
Subject: Re: [Talk-us] proposed first principles for United States road tagging

At 2010-03-04 09:38, McGuire, Matthew wrote:
>...
>A road's Observed Character is what kind of road it appears to be to a
>person on the road. For general purpose maps, using observed character to
>classify the roads intends to match a person expectations to what they see
>on the ground. Character is highly correlated with function, but is not
>the same.
>
>I think Observed Character is what OSM is trying to achieve with the
>highway tag. I think this because the OSM tag descriptions for highways
>have photos and describe how the road looks, and you cannot determine
>system or function from a photograph.  I also think it is what the Census
>Feature Class Code definitions describe.

I disagree. Even if this is what was intended, it's certainly less useful
than the others. When I zoom out a certain amount, what I want to see is
the local (aka residential in OSM) roads disappear. Further out still, I
want to see the tertiary roads disappear, etc. This is what's useful when
trying to map a route through an unknown area - you want to stick to the
main roads that get you there with better road conditions, fewer
intersections, etc.

As an example, in this area:
http://www.openstreetmap.org/?lat=34.426&lon=-117.664&zoom=11&layers=B000FTF
, 2-land paved roads are few and far between, making them important
tertiary or secondary connections. A road with the same characteristics in
the city would be unclassified, as there are much better roads. It's all
relative to the area, which is why I don't think it's reasonable to
classify by any objective characteristics - you have to know or survey the
area in order to know how to classify them. Perhaps some people with a lot
of experience may be able to do this from satellite imagery.

I believe this closely matches what I see in transportation sections of a
city's general plan. I think it's useful to use these as guidelines when
classifying roads. Many cities/counties of any reasonable size make these
available on their website. They usually have:

- freeway, expressway, etc. = OSM motorway or trunk
- primary arterial = OSM primary
- secondary arterial = OSM secondary
- minor arterial and/or collector = OSM tertiary
- local = OSM residential or unclassified

--
Alan Mintz <Alan_Mintz+OSM at Earthlink.net>


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