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2009年1月25日日曜日

[OSM-talk] When is a bridge not a bridge?

bridgeタグについての論議です。私も橋の橋梁部分にポイントを落とす際に悩む事は度々あります。何度か都市部の大きな橋で橋の境があいまいになりました。ここではLayerタグを使っての表現についても議論されていますが、Layerタグによる表現手法は便利ですが、使いすぎると整合性が難しくなると思います。
80n to talk
David
Was there a specific purpose you had in mind that needs to distinguish between the main span of a bridge and it's ramps, or were you just exploring the level of consistency in current tagging practices?
I wonder if we are approaching this problem from the right direction.
There are currently about 250,000 ways that are tagged bridge=yes. Since there's no generally agreed definition of the extent of a bridge every user will have used a different assumption and their own judgement.
Perhaps we should keep the vague and approximate definition that the bridge tag provides, and instead propose extra tags that more precisely define the lesser characteristics of a bridge. The bridge tag as it currently exists, for all its vagueness, is easy to use and effective.
For more precision we could consider additional tags that precisely define the individual parts of a bridge. The addition of a bridge_ramp tag, for example, could be used to indicate whether or not a bridge includes or excludes the ramps.
bridge=yes, bridge_ramp=includedexcluded
For those that want to define the extent of the ramps specifically then a separate way would be required for each ramp and for the main span, perhaps like this:
bridge=yes, bridge_ramp=yesbridge=yes, main_span=yesbridge=yes, bridge_ramp=yes
However, I'm not sure such an elaborate scheme would catch on much unless there's a real benefit in tagging bridges to a greater level of detail. That's why I wondered whether you have a specific reason for wanting to tag bridges with more precision.
80n

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