[OSM-talk] Bridges / viaducts for railways

[Andy Robinson (blackadder)]

matthew-osm at newtoncomputing.co.uk wrote:
>Sent: 28 January 2008 7:01 PM
>To: Tom Chance
>Cc: Talk Openstreetmap
>Subject: Re: [OSM-talk] Bridges / viaducts for railways
>
>On Mon, Jan 28, 2008 at 05:57:24PM +0000, Tom Chance wrote:
>> I'm a bit confused about these tags:
>>
>> railway=viaduct
>> bridge=yes
>> cutting=yes
>> embankment=yes
>>
>> Why is it not a property like bridge, cutting etc. and will it render
>> correctly? Should it be changed to viaduct=yes?
>
>Ewww, yuck... boolean flags.
>
>Personally I would tag as:
>
>  railway=rail
>  bridge=viaduct
>

bridge and viaduct are two separate types of structure so strictly speaking
bridge=viaduct is incorrect.

>for cutting I would have thought more like (this is a suggestion, there
>is probably a better way):
>
>  railway_level=-1  or  railway_level=cutting
>
>and for embankment
>
>  railway_level=1  or  railway_level=embankment
>

We already use layer=+/-5 for setting display layering and I always
envisaged the same simple system could be used for cuttings and embankments.

>Map features has the really odd (IMO):
>
>  railway=viaduct (node)
>  highway=viaduct (node)
>

I think these are legacy from when I first put up map features when we
didn't have ways and all that and I wanted some method of showing a viaduct
icon. Could be wrong. No harm in leaving this as the tag for a node though.

>with the comment of something like "A high or long bridge...". "long"
>and "node" don't go together as far as I am concerned ;-). You also don't
>know what type of railway goes over the viaduct, as you lose the railway=
>information.
>
>A possible, but slightly odd, example would be an underground train going
>above ground and over a viaduct - it would be railway=subway,
>bridge=viaduct.
>If memory is correct, I think the DLR does that in some places in London
>(railway=light_rail, bridge=viaduct)?
>

I'd prefer to see railway=rail for all rail corridors and a secondary tag
for the type of service/stock used - ie metrorail/subway/underground/freight
etc etc etc

But it's no big deal to understand what's implied without extra tagging.

Cheers

Andy


>Not sure what others do, though...
>
>Cheers,
>
>--
>Matthew
>
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