[Talk-GB] Sorting out layering in East Anglia, Essex, London and Kent

Peter Miller peter.miller at itoworld.com
Tue Apr 19 15:21:41 BST 2011


On 19 April 2011 14:50, Andy Allan <gravitystorm at gmail.com> wrote:

> On Tue, Apr 19, 2011 at 2:31 PM, Peter Miller <peter.miller at itoworld.com>
> wrote:
> >
> > Andy Allan just asked me a question privately about changes I have made
> to
> > layers in Wandsworth which has prompted me to do a post here saying what
> I
> > have been up in order to rationalise use of the layers in East Anglia,
> > London and now Kent.
> >
> > The ITO Map 'Layers' view highlighted a huge amount of weird layer tags
> in
> > the area. London seemed to be particularly bad. There were parks at
> layer-5
> > and lakes at layer 1; railways at layer=1 or -1 even though they were on
> the
> > ground.
>
> So my concern was that data is being removed for no particularly good
> reason. For example, at
>
> http://osm.org/go/euum@dsaa--
>
> the two central carriageways were tagged layer=-1 to show they are
> below the nearby sliproads, but Peter has removed these layer tags.
> I'm assuming his map layers view has some logic that layers tags only
> apply to ways that cross but I don't believe that to be true. He's
> also removed the layer tags from stretches of the railway, for example
> at
>

To my mind the lower road is at 'modified ground level' which is layer=0
which is optional.

It it is in a cutting the the 'cutting' tag would be appropriate. because
the layer tag saying nothing about relative height to a parallel way, only
about the z ordering at crossing points. Consider the path that the top and
bottom of the Grand Canyon both of which are at 'ground level'.

>
> http://osm.org/go/euunor2Ku--
>
> which again, those of us who know that area know the railway is on a
> different layer to the surrounding roads. While there is an argument
> in both cases that there could be additional methods of tagging the
> situation (such as adding embankment or cutting tags) I still don't
> see that removing the layer tags is doing anything other than removing
> the correct information that was there previously.
>

Since the railway crosses the Old York Road then I believe that there should
indeed be a bridge (with a layer tag). Adding a layer tag for the full
section of track and not having a bridge is not the right answer.

If the whole section of railway is up on a concrete platform then it may be
more appropriate to use a viaduct for the whole section but that does not
seem to be the case from Bing. If it is raised up on a bank then an
embankment may be appropriate. However... the layer tag is not the right tag
to use and doesn't give any of that information.

On balance I think bridge is right for the section over the road. I failed
to add that bridge section  - sorry about missing that one. Make that 101
bridges!

It may well be good to add an embankment tag to the section between the
bridges.



Regards,


Peter


> Cheers,
> Andy
>
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