[OSM-talk] Layers query

[Andy Robinson]

Tom Chance wrote:
>Sent: 08 October 2006 1:10 PM
>To: talk at openstreetmap.org
>Subject: [OSM-talk] Layers query
>
>Ahoy,
>
>Can somebody confirm how one should use the layer attribute? The wiki says:
>
>layer   -5 to +5     Use also for display order
>
>So if I have, for example, a footbridge over a railway, do I add "layer=1"
>to
>the footpath way, and leave the railway at a default (assumed) value of
>zero?
>That seems to work with osmarender.
>
>Would it be a sensible convention to use negative values if the way goes
>underground, and positive if the way goes over a ground-level feature? So
>the
>footbridge gets "level=1", and an underpass under a railway would
>get "level=-1" rather than adjusting the railway. That of course doesn't
>make
>sense for lakes and rivers in parks, which should be "on top" of the park,
>but the convention can be flexible.
>
>If there's a consensus on this I'll add an explanation to the wiki, just to
>make it perfectly clear.
>

Tom,

As you suggest, I considered the negative values for underground (including
cuttings) and positive for above ground. However I never went any further
than this concept so I'd be interested in hearing other views on how this is
best implemented or if another format is preferred.

At the time we were not using areas so I really didn't think about a display
order for them at all.

There is an argument to say that the footbridges and underpasses should be
tagged with some sort of relative elevation tag, whereas areas inside areas
would be tagged with a display order tag (layers is ok).

Is a distinction between these two logical differences necessary, or not?

Cheers

Andy Robinson
Andy_J_Robinson at blueyonder.co.uk


>Regards,
>Tom
>
>--
>The struggle against power is the struggle of memory against forgetting
> - Kundera
>
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