[Talk-us] highway: tertiary?

[Alan Brown]

I noticed the following suggested definitions for California for different road classes:

http://wiki.openstreetmap.org/index.php/California


For tertiary, they suggested


highway=tertiary
Lower traffic volumes on wide streets, or higher on narrow ones. 


Kinda' vague ....   and I'm not sure I'm in agreement with these definitions, personally.  I'd be even more vague :) .  Here's what I think as someone who worked in a map data company for a decade:


Navteq and Tele Atlas have something known as a "functional road class" that is used to designate the relative importance of a road for getting to your destination.  During a typical trip, you would progress from roads of less-important functional road class, to more-important fucntional road class, and back down to less-important functional road class as you reach your destination.  I would guess, within a mile of most urban origins, you'd expect to be on a "tertiary" road, and within another mile you'd find yourself on "secondary" road, and so forth. (Of course, if you can get to a more important road quicker, you'd use that.)

Point to be made is, the functional road classification of a road might not strictly reflect the physical attributes of the road (number of lanes, speed limit, etc.) but rather, the relative importance of a road in its particular vicinity.  The clearest example of this I can think of is the Transcanadian Highway.  There are portions of the Transcanadian Highway that are not limited access, due to low population densities.  However, Navteq gives it the "most important" classification level - while some Interstate Freeways, and many local limited access freeways in the US, are not assigned to that category.

Point to made is, commercial data providers are somewhat subjective in their assignment of "functional road class".  Open Street Map's "Highway" attribute may be a bit different:  certainly, a
"Motorway" is a clearly defined type of road.  However, when I've assigned "Primary", "Secondary", or
"Tertiary" categories, I've tried to use local knowledge to reflect what the relative importance of those roads are.   It will tend to track the physical attributes of the road, but not strictly.  Some of it's aesthetics - I'll try to decide which primary roads should be demoted to secondary roads if the map starts looking too cluttered, or try to promote some roads from tertiary to secondary if the map looks too thin.  Perhaps one secondary road between each pair of primary roads, and one tertiary road between each pair of secondary roads (although that's impossible to it exactly like that.)

San Jose (where I live) has a lot of physically wide roads with moderately high speed limits that aren't used nearly as much as other roads with the same characteristics.  Use the highway attribute to reflect that reality.  Use explicit attributes to define number of lanes and speed limit.

It's subjective.  A Tele Atlas map and a Navteq map based on functional road types will look different because they made different judgements.  (They do have rules to eliminate some of the subjectivity - but not completely.)


That's my opinion - anyone disagree?




----- Original Message ----
From: David Carmean <dlc at halibut.com>
To: talk-us at openstreetmap.org
Sent: Saturday, September 13, 2008 9:48:35 PM
Subject: [Talk-us] highway: tertiary?


Hi,

I'm not sure if this question is within scope of this list, but 
I thought it might be sufficiently country-specific:  when is it 
appropriate to use "highway: tertiary" in the US?

Thanks.


_______________________________________________
Talk-us mailing list
Talk-us at openstreetmap.org
http://lists.openstreetmap.org/listinfo/talk-us
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstreetmap.org/pipermail/talk-us/attachments/20080913/988729c4/attachment.html>