> I still do not understand why area=yes is a bad tag...

> you have problems to implement it in your workflow.

That is not correct. It is simple enough to check for the presence or
abscenss of `area=yes` prior to rendering. See an attempt at
https://github.com/gravitystorm/openstreetmap-carto/pull/3834 (Though
I now realize that this PR did not properly account for multipolygons
relations).

The problem with relying on `area=yes` for deciding how to render a
feature like a hedge or wall is two-fold:

1) The tag `area=yes` is only supposed to mean "this closed way is an
area, not a line", and is only used when this is not already obvious
from other tags.

It is not necessary to add `area=yes` when the closed way already has
a tag which defines an area, such as `landuse=forest` or
`natural=scrub` or `leisure=playground`: all of these keys are always
areas when mapped as closed ways, so they do not require `area=yes`,
whether or not `barrier=hedge` or `barrier=fence` is added.

This also means that `area=yes` is never needed when the same object
is turned into a multipolygon relation, so checking for `area=yes`
alone is not sufficient

A closed way with `hedge=barrier` + `natural=scrub` is an area, and
the presence or abscense of `area=yes` should not be required. This
makes this a poor tag to rely on for rendering decisions, at least for
a style that influences how mappers use tags.

2) Many hedges which were mapped like areas are currently missing
`area=yes` tags. In this comment
(https://github.com/gravitystorm/openstreetmap-carto/pull/3844#issuecomment-582692389)
you can see that over 90% of the `barrier=hedge` closed ways in a
Dutch province (random example) are missing `area=yes`, though they
appear to be mapping the outline/area of the hedge. This means that a
rendering solution that relies on `area=yes` would miss a large
percentage of hedges mapped in this way. The situation is worse for
barrier=wall.

Most likely, many mappers do not see why they should need to add a tag
like `area=yes` when they map a hedge as a closed way.

A better solution is to use different tags for linear features and
area features. This is the standard used in Openstreetmap for common
linear features such as paths, roads, railways and waterways: the area
and the line are different tags.

(The rare exception to the rule that the same tag isn't used for lines
and areas is for pedestrian plazas which are mapped with area=yes, but
in this case the idea is that there is no linear feature: the area
allows travel in "any" direction by pedestrians, so there is no "line"
to map, just the area. Yet there often is confusion about how
pedestrian highway areas should be mapped and how they differ from
area:highway=, so this cannot be considered a good example to emulate
in the future. )

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