[Tagging] Barrier=berm

[Volker Schmidt]

I see a number of problems with the proposal

   - First of all when I see a both-sided sloped linear elevation I do not
   know I see a berm.because it is a rarely used term
   - Second it is ill-defined from the shape point of view: it can define a
   step in an earth wall and it can mean an earth wall with sloped sides
   - Third it is also ill-defined from the purpose point fo view - see the
   Wikipedia article.
   - Fourth it can describe man-made or natural objects.


Let's go back and define what we need
I think we need a way  to describe a man-made linear structure that is
higher as the surroundings, has slopes on both sides..
We need to be able to represent in a simple form smaller items, say with a
width in the range of up to 10 meters and big ones in the tens of meters
range for width, where we need to be able to map the footprint (often
visible from satellite photos, and the edges of the top if the top is flat.
Then we need to tag the surface material,and, if known, the material from
which the structure is made.
And we want to indicate the purpose.

There are many types of objects with completely different purposes that
spring to mind

   - Sound.deflection structures
   - military defensive structures (mostly historic)
   - water-defence structures (The levee in the photo
   <https://commons.wikimedia.org/wiki/File:Levee_of_the_River_Po.jpg> is
   typical. It's base is clearly visible form satellite photos and is 60m wide)
   - explosion-risk containment structures
   - water containment structures


What we have

   - embankment=yes on a way to say that it sits on top of a raised
   structure on both sides (this tag is purpose-free)
   - man_made=embankment is a directional way which indicates that marks
   the upper edge of a downwards slope (this tag is purpose-free)
   - man_made=dyke which is similar in shape to embankment=yes, but has a
   purpose as well: flood protection (also known as levee)
   - waterway=dam which can shape-wise be similar to a dyke, but for a
   different purpose.
   - land_use=basin defines a structure which often uses dams


Thinking about it we may only need to add a new man_made=slope_base tag.
Packaging this together with the opposite man_made=embankment in a "slope"
relation, this would give us the possibility to model even complex objects.
Without a relation a closed  man-made=slope_base way could be used to draw
the footprint of levees/dykes. The use could be similar to water=riverbank.

Volker
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