[Talk-TW] Fwd: [OSM-talk] Key:layer update

[李昕迪 Lee, Sin-di]

"the natural ground level as it would be shown by contour lines on a
topographic map"
所以河流的 layer 算是 0 囉？

有些 map feature 被強制需要加上 layer 得 tag

還有更多討論在原討論串

---------- Forwarded message ----------
From: Richard Z. <ricoz.osm於gmail.com>
Date: 2014-03-09 18:30 GMT+08:00
Subject: [OSM-talk] Key:layer update
To: talk於openstreetmap.org


Hi,

for some time now I have been working on the wiki page to state the rules
as clearly as possible.. hope that most of the improvements are fairly
uncontroversial. Some of the changes:

* the vertical ordering established by the layer values is valid exactly only
  in the point where the ways cross or objects overlap

* define layer as higher value means above, lower value means bellow. Avoid
  the complicated layer=0 definition as "the natural ground level as it
  would be shown by contour lines on a topographic map". Explicit layer=0
  seems to be deprecated now.

* layer on ways should be used only in combination with one of
tunnel=*, bridge=*,
  highway=steps, highway=elevator, covered=* or indoor=yes. For areas, it could
  be used in combination with tags such as man_made=bridge, building=*
and similar.
  The motivation for this is to make it easy for validators to spot errors such
  as when the wrong segment is accidentaly tagged, bridge/tunnel forgotten, or
  someone tags excessively long ways for no good reason - common problem with
  waterways and elevated roads/railroads.
  I have validated this rule for ways in large parts of the world, there are
  exceptions which currently I do not know hot to tag better but those are rare.

* in some cases "level" may be more appropriate than "layer"

https://wiki.openstreetmap.org/w/index.php?title=Key%3Alayer&diff=999107&oldid=935491


Richard

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李昕迪 Lee, Sin-di | http://www.mcdlee.tw