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 [EMAIL PROTECTED]
To: talk-us@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@openstreetmap.org
http://lists.openstreetmap.org/listinfo/talk-us
___
Talk-us mailing list
Talk-us@openstreetmap.org
http://lists.openstreetmap.org/listinfo/talk-us
