[Talk-us] Excess TIGER nodes in a way

[Alan Brown]

I can say what I do ...
First I'd verify that there's no extra information attached to nodes that I'd consider deleting.  :)
Then I'd make a judgement:  as the nodes are positioned now, do they make the road look a little "crooked" in a way it really isn't?  If it does, I start thinning.  The nodes are eating up space in the database, but are not contributing to the quality of the information.  
If it has more nodes than necessary, but it's straight as an arrow - I usually leave it alone.
On a dual carriageway, it usually improves the appearance if you position the nodes on each side at the same position.  This makes it easier to keep the carriageaways a constant distance apart.
Another rule of thumb - if the nodes do not represent something physical (such as a junction of two roads) - the tighter the radius, the more nodes there should be per unit distance.  But even for straight roads, I think it's good to maintain a maximum distance between nodes - perhaps a mile.
If you keep nodes too far apart, moving one node will impact something that's far away.
By the way, the biggest value in rendering roads as a dual carriageway, is that it provides a natural way to express a lot of information about physical turn restrictions; it's not just for appearance.  Be careful about how you connect cross streets - if they connect to both carriageways, connect the cross street to both via nodes.  If it's an underpass or overpass, connect nothing.  If it just connects to one carriageway, connect to it.
-Alan



----- Original Message ----
From: Joseph Scanlan <n7xsd at arrl.net>
To: Talk-us at openstreetmap.org
Sent: Thursday, August 21, 2008 10:10:52 AM
Subject: [Talk-us] Excess TIGER nodes in a way

There's a question at the end but I'll start with a little background.

Last weekend I took a drive that included US 93 in Arizona.

Naturally, I wanted to compare my GPS trace, the Yahoo images, and my 
memory to the OSM data.  Much of this piece of US 93 is divided highway 
(is this also called a double carriage way?) but the TIGER data in OSM 
shows a single primary way.  I moved the existing way to the northbound 
side of the highway and drew a fresh southbound way.  They are both 
tagged "highway=primary", "oneway=yes", "ref=US 93", and "name=United 
States Highway 93".  The TIGER tags remain on the northbound side but 
are not duplicated southbound.  So far I'm happy with this.

Parts of this highway are quit straight:

    http://www.openstreetmap.org/?mlat=35.396938&mlon=-114.259680&zoom=14

The northbound way has (mostly) all the nodes from the TIGER data. 
Southbound only has as many as I needed to connect to other ways, copy 
the shape of the northbound way, and a few more where a northbound node 
might have marked something in the image but there wasn't a way in the 
data.  This part bothers me.

Now the question.  Should I 1) delete the (what I believe are) extra 
TIGER nodes from the northbound way, 2) add a bunch of nodes to the 
southbound way to make it match northbound, or 3) call it done and learn 
to be happy?

-- 
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Joseph Scanlan                              http://www.qsl.net/n7xsd
+1-702-455-3679                              http://n7xsd.dyndns.org
jps at co.clark.nv.us (work)                  (not work) n7xsd at arrl.net
---------------------------------------------------------------------

So he went inside there to take on what he found.
But he never escaped them, for who can escape what he desires?
                                              --Tony Banks of Genesis
                                                    in "The Lady Lies"

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