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

Roy Wallace waldo000000 at gmail.com
Thu Oct 1 22:41:50 BST 2009

On Thu, Oct 1, 2009 at 9:35 PM, David Earl <david at frankieandshadow.com> wrote:
>> Ah, so are you saying that, in Martin's attached image, the red way
>> and the yellow way should/could meet at the junction? If so, then IMHO
>> it is even *less* clear that, e.g. traveling from the red to the grey
>> way is a left turn, whereas traveling from the red way to the yellow
>> way is uninterrupted.....
> No I was referring to the real examples I quoted.

A picture would help my brain...sorry.

>>> I think anyone looking at it would understand the arrangement on the
>>> ground,
>>> and it does model the situation as I see it.
>> Don't be fooled - people are not the only ones that "look" at OSM data.
> I don't understand this at all. I am just mapping what I see on the ground.
> And please don't patronise, I'm well aware of the uses of OSM data and have
> contributed to many of them.

Apologies if that came across patronising - I really didn't mean it
that way. My point is that IMHO mapping so that it is understood when
looked at by a person is not sufficient (as, it seems, you're already
well aware).

> The main road goes round a corner (and may or may not share the same name).
> I represent the corner even though there may be a straight kerb line on one
> side, when curvature exists e.g. on the opposite kerb or in the white
> lining.

That's all fine. I'm just saying that *doesn't* indicate that
following the curved road *doesn't* constitute a turn.

> In English I think I'd want to be told "follow the road round to the left"
> or some such in these circumstances, not a simple "turn left".

Exactly - for software to be able to say, e.g. "follow the road around
to the <left/right>", the mapper needs to be able to map
"continuations of roads at junctions". This can be done explicitly,
using the methods (relations) I described. Using a curve does not do
this explicitly.

> A T junction
> certainly wouldn't achieve that possibility without more information. An
> explicit tagging would. But in the absence of that, modelling what's on the
> ground goes some way.

We agree here. Modeling what's on the ground (e.g. curves, etc.) goes
some way, but does not answer the original poster's question. For
that, we seem to agree that we need explicit tagging. What did you
think of my suggestions?

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