[OSM-talk] Clarifying and representing road markings at junctions

David Earl david at frankieandshadow.com
Thu Oct 1 11:05:55 BST 2009

On 30/09/2009 22:05, Roy Wallace wrote:
> On Wed, Sep 30, 2009 at 7:35 PM, David Earl <david at frankieandshadow.com> wrote:
>> On 30/09/2009 10:20, Martin Koppenhoefer wrote:
>>> you could model it like this (see attached, colours are just
>>> indicating the ways, not highway-classes)
>> Yes, that's also what I typically do, e.g.
>> http://www.openstreetmap.org/?lat=52.596517&lon=0.376144&zoom=18&layers=B000FTF
> Eek. Nice hack, but dodgy...
> 1) What if the road name changes *at* the junction, not just after the junction?
> 2) That hack just seems to change two things:
> a) it changes the *angle* between the intersecting ways at the
> junction. Is there any reason to want to do this? What exact problem
> does it solve?

It's not a hack, it's a very reasonable representation of what's on the 
ground. The kerb line may be straight on one side but is usually curved 
opposite the junction, and many such junctions now have a build out 
which reinforces the curve around the corner, but even if it isn't the 
centre line curves around the corner, and often the give way lines as well.

It shows visually which the "main" road is at the junction and is a good 
model of the physical arrangement.

> b) it makes a single *way* continue through the intersection. 

err, no. If the road has the same name around the corner it can do. If 
the minor but straight on road has the same name it could be a 
continuous way, but I would normally break it at that point, not least 
so the name of the "minor" road is clear. But where ways break is of no 
significance - you have to break ways at all sorts of places because of 
changes in the environment like speed limits, starts of bridges etc.

> Does
> this actually infer that there is no giveway instruction? 

Not necessarily, though there nearly always is.

> If so, is
> this documented anywhere? (I'm sure I could find examples where this
> is not the case) If not, then the hack *doesn't* explicitly show that
> the curved road continues through the intersection without
> interruption.

I think anyone looking at it would understand the arrangement on the 
ground, and it does model the situation as I see it.

It is very unusual indeed in the UK anyway to find a case where priority 
is around the corner but there is no curvature at all in the way it goes 
around the corner. If there really is no curve whatsoever (and I can't 
think of an example off hand that I've mapped in 3 years of mapping, 
though I'm sure there are some), then I wouldn't try to model a curve. 
It's not a hack, it's what's actually there to a greater or lesser 
extent in most such circumstances.


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