Reduce way_pixels limit to >750 for protected_area boundaries

[jeisenbe]

Changes proposed in this pull request:

• Renders national_park, nature_reserve, protected area, and aboriginal_lands boundaries at >750 waypixels instead of >3000.
• This causes the boundary outline to render 1 zoom level sooner than the name label for these areas. The text label renders at >3000 waypixels.
• This is also the same limit that is used for tourism areas, such as zoos and amusement parks, with outlines. (Military areas and police stations currently render with > 900 waypixels, similar to the number in this PR.)

Explanation

• Currently, boundaries for protected areas, national parks, nature reserves and aboriginal_lands are only shown when the polygon is rather large: 3000 square pixels, approximately. For example, a 31 by 101 pixel rectangle will render, but a 30 by 90 pixel polygon would not show the borders at that zoom level.
• 3000 square pixels is also the same limit used to show the text label, because it should usually be large enough the fit the name within the area (though this depends on the shape of the area and the length of the name). This means that the area is not visible until it suddenly appears at a moderately large size, with a name.
• Previously, tourism areas (zoos and theme parks) were changed to render at 750 way_pixels; this is 1/4 of 3000, so it is 1 zoom level sooner. For example, a 25 x 30 pixel polygon is 750 pixels square. This means the outline normally appears one zoom level before the name (if there is a name). See Hide tiny zoos and theme parks #2835
• It's logical to render this boundary lines with the same rules, so that the area will be shown one zoom level sooner than the name.

Test rendering with links to the example places:

Lake Gilles, South Australia
https://www.openstreetmap.org/#map=9/-33.0317/136.9267
Before: z8

z9

After: z8

z9

Singapore
https://www.openstreetmap.org/#map=13/1.3804/103.8138
z12 Before

z12 After

Sungei Buloh
z13 Before

After: z13

z14 same

Chestnut Nature Park (left)
z13 Before

After z13

z14 same

[kocio-pl]

This would partly revert #2119, but that should not be a big problem:

• I like the idea to make it similar to other areas
• 750 instead of 3000 is still bigger than 100
• we had also some tuning of protected areas borders lately in Nature reserve boundaries revision #3574, especially on z8 and z9, where the problem is the most severe

[kocio-pl]

Seattle example:

Old rendering from #2119 (comment)

Current rendering

Proposed rendering - the missing pieces inside are now back, while borders are no longer screaming

[kocio-pl]

Warsaw example:

Old from #2119 (comment)

Current

Proposed

[jeisenbe]

Thanks for the additional test renderings! I hope this is a good compromise.

…

On Tue, Feb 5, 2019 at 1:13 PM kocio-pl ***@***.***> wrote: Warsaw example: Old from #2119 (comment) <#2119 (comment)> [image: aq2tiysm] <https://user-images.githubusercontent.com/5439713/33798107-4d93379a-dd13-11e7-84b4-396f25392785.png> Current [image: screenshot_2019-02-05 openstreetmap carto kosmtik 2] <https://user-images.githubusercontent.com/5439713/52252706-440fb980-2904-11e9-90a7-26e6ea27b1a8.png> Proposed [image: screenshot_2019-02-05 openstreetmap carto kosmtik 3] <https://user-images.githubusercontent.com/5439713/52252708-470aaa00-2904-11e9-89f3-3b83c4bee049.png> — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#3661 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AoxshOjgLE957lLyopsQT-A_rX-Z_SGpks5vKQTRgaJpZM4aaK6A> .

[kocio-pl]

Syracuse example:

Old from #2119 (comment)

Current

Proposed

[kocio-pl]

I hope this is a good compromise.

Both US examples are extreme and they still look sane now, so yes, I think so.

Thanks for making and explaining this unification.

[jeisenbe]

Both US examples are extreme...

It looks like the issue in those areas is that there are some moderately large protected_areas (wilderness or state forest?) which have many small outlying parcels, so it looks odd when these suddenly appear. If they were separate protected areas, they would not be render for another 2 or 3 zoom levels.

Since the way_area is based on the whole multi-polygon, we can't easily render the outline for only the largest polygon without also rendering the tiny outlying polygons.

For text labels, there's a property text-min-path-length which allows us to "Place labels only on polygons and lines with a bounding width longer than this value (in pixels)". Also there's text-largest-bbox-only which by default only labels the largest polygon in a multi polygon with a text label.

We could ask the Mapnik developers if they could consider adding a similar feature for polygon fills and outlines?

[kocio-pl]

Sure, please do.