Show national park boundaries from higher zoomlevel and larger size

[matthijsmelissen]

With this commit, national park boundaries will be shown from the
same zoomlevel and size as their label, effectively eradicating
small unlabelled national parks from the rendering.

Such small national parks seem to contribute to a crowded feel of
the map in the areas and zoom levels where they occur.

[pnorman]

I prefer showing the parks too small to fit a label in

[imagico]

IMO neither of these looks good, displaying national parks at this scale in this way seems to be causing more harm than have advantages.

In the US a lot could be gained by dissolving the inner boundaries and essentially showing the protected area as a whole - still keeping the labels but without indications where one park ends and another starts - which is confusion at this scale anyway.

But this would not solve all of the problems related, especially the color distortions of other elements through the semitransparent fill and border and the color confusion with natural=wood.

[pnorman]

I think completely changing the national park rendering is outside the scope of this PR

[matkoniecz]

I prefer showing the parks too small to fit a label in

I also share this opinion, I think that this change makes situation pretty confusing.

[matthijsmelissen]

I am re-opening this PR. I think the amount of small nature reserves is still a big problem. The number of places where rendering them looks good is greatly outnumbered by the number of places where they cause a problem.

[matthijsmelissen]

Rebased.

Note that the change in zoomlevel has been merged before.

[matthijsmelissen]

Can anybody review this (again)?

[kocio-pl]

I think it is useful to start with that. I want to add boundary=protected_area later and use different zoom levels too (see #603), but that can take me some time.

Example (click to see the full size):

z8
Before

After

z9
Before

After

[kocio-pl]

Another example - near Warsaw:
Before

After