Render bare_rock pattern from z13, same as shingle and scree

[jeisenbe]

Fixes #3862

Partial revert of #3458

Changes proposed in this pull request:

• Renders rock_overlay.png pattern from z13 only, instead of z5, for natural=bare_rock
• This is the same level when the similar features natural=scree and natural=shingle are first distinguished from natural=bare_rock by a pattern.
• At mid and low zoom levels the great majority of bare_rock areas are too small for the pattern to be clearly seen, but the pattern adds noise and makes it harder to interprete the outline of these areas. For this reason, the pattern is not shown for scree or shingle before z13 (similarly, scrub, forest and other patterns are not shown before z13).
• Currently the only very large areas of bare_rock are coarsely-mapped desert areas, which really consist of a mix of sand, scree, bare_rock, heath, grass, etc, and our showing the pattern early gives unintentionaly encouragement to mapping really large areas like this coarsely, rather than showing the detailed landcover/surface in each spot.

Test renderings with links to the example places:

Wales - NW

• Most areas of bare rock in Wales are small patches on peaks or near quarries or along the ocean, as in most of Europe.

https://www.openstreetmap.org/#map=12/53.0707/-4.1940
z13 - unchanged

z12 before

z12 after

z11 before

z11 after

Wales - Snowdonia National Park

• This is by far the largest area of bare_rock in Wales
  https://www.openstreetmap.org/#map=13/52.9000/-4.0023

z13 Unchanged

z12 before

z12 after

z11 before

z11 after

Corsica - South

• Like most of Metropolitan France, Corisica has somewhat complete landcover mapping from imports, so it's not very high resolution.
• This is the largest bare_rock area in Corscia:
  https://www.openstreetmap.org/#map=12/41.6185/9.1643.png

z13 same

z12 before

z12 after

z11 before

z11 after

Corsica - North

• These areas of bare_rock are average-sized for Corsica
  https://www.openstreetmap.org/#map=12/42.5801/9.3068

z13 same

z12 before

z12 after

z11 before

z11 after

[kocio-pl]

On the one hand I understand this as a rule, but in practice pure color areas look cryptic to me. For example in Snowdonia National Park z12 looks like industrial areas and on Corsica this looks similar to military area color nearby.

[jeisenbe]

in practice pure color areas look cryptic to me

That's how we render natural=scree and natural=shingle currently. I would be happy to adjust the low zoom @bare_ground color to improve it, however.

That's done in #3670, where unvegetated areas are rendered as #efe7d9.

The current rendering is lightened 20% at low zoom, so it looks a little too similar to some other features.

[imagico]

I think this is fine - adjusting the low zoom color for the bare ground areas could be considered - but this makes relatively little sense as long as the fading is messing with the color relationships anyway.

[kocio-pl]

I would be happy to adjust the low zoom @bare_ground color to improve it, however.

Since brown looks more or less like a mud, I expect that might be hard without the patterns. But of course one should see test such assumptions.

[jeisenbe]

Since brown looks more or less like a mud...

We currently use earth-tones ("brown") for:
@farmyard: #f5dcba
@garages: #dfddce
@construction: #c7c7b4
@heath: #d6d99f

In addition to @bare_ground: #eee5dc (scree, shingle, bare_rock)
and
#e6dcd1 @mud

And before we had the earth-tone @societal_amenities color (previously the old @farmland color)

I don't think those ALL look like mud, do they? ;-)

[kocio-pl]

I have never seen a garage area being THAT big... We don't expect to see anything like this on these levels and there are relatively few types of objects, so it's much easier to find better fitting colors.

Another idea might be to mix background brown with some grey taken from the pattern. Mud could be more brown and less grey, since this is basically a soft (watered) ground. In general, it seems that bare ground and mud are currently "flipped", so maybe just flipping them would be enough.

[jeisenbe]

How about #efe7d9? This was tested in #3670 - I could show some examples from that branch.

(But any changes to the fill colors will need to be in another PR, whether in #3670 or a follow-up)

[imagico]

Works as intended and restores the previous state and with that the last remaining pattern use at low zoom levels (together with wetland - see #4094).