[Tagging] Difference between barrier=embankment and man_made=embankment?

[Paul Allen]

On Wed, 29 May 2019 at 13:42, Christoph Hormann <osm at imagico.de> wrote:

>
> man_made=embankment is almost exclusively used for one-sided artificial
> slopes - prominently supported by OSM-Carto rendering it this way.
>

That surprises me.  Not that either man_made or barrier was used for
one-sided artificial slopes but that a one-sided slope is considered an
embankment.

It's not even clear to me that something counts as an embankment if it is
not
higher than the ground on both sides.  Not necessarily the same height
difference
on both sides, but a difference nonetheless.  Otherwise it's just a slope.

barrier=embankment is in the relatively small volume of use mostly used
> for symmetric structures with slopes on both sides.
>

That may be more an artifact of which tags are used by editor presets for
embankments.  I believe iD changed from barrier to man_made fairly
recently.

The thing is that railway embankments are man-made and their purpose is not
to act as barriers.  But fortifications, whilst also being man-made, are
specifically
intended to be barriers.  I'm not entirely convinced we should be
deprecating either
tag, but man_made is more generic so if we must restrict ourselves to one
tag
then that is the one.  I think we throw away some detail if we restrict
ourselves to
man_made, but we would be deceptive if we tagged railway embankments as
barriers.


> And current tagging documentation does not provide a clear suggestion
> how to tag such - if with embankment=yes as a standalone tag or with
> man_made=embankment + embankment=both or embankment=two_sided.
>

For me this is somewhat similar to the difference between a wall and a
retaining wall.
Retaining walls, by their function, have a significant height difference
between the two
sides.  Economics may mean the height difference on one side is so small as
to be
negligible.  Ordinary walls have no such difference (or perhaps no more
than a centimetre or
two).  To my mind, embankments are two-sided just as non-retaining walls
are.

Consider a "one-sided embankment."  What would things look like if the
embankment had
not been constructed?  The drop from high to low shifts position a metre or
two.  A different
angle of slope, maybe. Without knowledge that there was an artificial
construct present,
you'd have no way of distinguishing the two situations just from simple
observation.  A
retaining wall is distinguishable because of man-made materials, but a
"one-sided
embankment" is not.

-- 
Paul
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