Central text labels for admin_level=6 features should be have higher priority than villages and suburbs

[c933103]

For a number of admin_level=6 features, like:
https://www.openstreetmap.org/node/6743291688 Kinmen, Taiwan
https://www.openstreetmap.org/node/60655851 Matsu Islands/Lienchiang, Taiwan
https://www.openstreetmap.org/relation/2410520 Gangnam-gu, South Korea
https://www.openstreetmap.org/relation/2409164 Gapyeong-gun, South Korea

They are considerably more important their underlying features and should render at a range of zoom levels where the name of these counties/districts would be useful, however at many zoom levels the OSM carto would render their underlying villages/area name instead of the more significant name of the county/district themselves.

Expected behavior

They are expected to be displayed more prominently than labels with admin_level=7 value in zoom level 7 to 14.

Actual behavior

They are not being displayed at all.

[jeisenbe]

We only recently started rendering a central text label for the names for admin_level=5 and =6 boundaries. See #4100

https://www.openstreetmap.org/relation/2410520 Gangnam-gu, South Korea is displayed at zoom level 13:

At zoom level 14 and higher the central label is not shown because the area is too large (it already takes up most of the screen, over 196,000 square pixels), but the name is rendered along the boundary:

z14

At z12 the label is blocked by the name of a place=village (perhaps this should be a place=quarter or place=neighborhood instead?), which is being rendered with higher priority: https://www.openstreetmap.org/node/415155293#map=13/37.4975/127.0657

Since many admin_level=6 features have the same name as a town or city, we decided to render the places with higher priority. This could be changed, but it would lead to poorer results in some countries.

(If this area, "Gangnam-gu", is also the well-known name of this part of the city, perhaps it should also be mapped as a place=suburb node?)

https://www.openstreetmap.org/relation/2409164 Gapyeong-gun is displayed at z10:

We decided not to show admin_level=6 earlier than z10, though in this case the area is large enough that we could have shown it at z9 as well. But in some countries this would make the map quite crowded, for example when admin_level=6 areas are small.

It doesn't render at z11 and above because the area on the screen becomes too large. Anything larger than about 400 * 500 standard pixels will no longer get the central text label, though at that point the name renders along the boundary line.

https://www.openstreetmap.org/relation/3777249#map=10/26.0389/120.2921 Matsu Islands is rendered at z10:

At z11 and higher the name is rendered along the boundary instead

For the other one, the problem is that the province (admin_level=4) takes up most of the same area, so it get's labeled instead.

Compare:
https://www.openstreetmap.org/relation/3777250#map=10/24.3990/118.3804 Fujian Province (Taiwan) vs
https://www.openstreetmap.org/relation/3339695#map=10/24.4365/118.4038

Since the 2 boundaries share the same area around the largest island, just the more important admin level is shown.

But if you zoom in to the border at higher zoom levels, you can see both names:
z11 Kinmen/Fujian

[c933103]

So they are now being rendered at center of relation instead of on the label node, and using a less prominent color than those villages/etc underneath? (Or are those actually features with place=* tags and they got rendered more prominently?)

[jeisenbe]

Previously only features with admin_level=2 or =4 (countries and provinces) had a name label rendered in the middle of the area at certain zoom levels, and places such as place=village and place=town have long been rendered at the location of the place= node.

Now administrative boundaries with admin_level=5 and admin_level=6 are also having these labels rendered at certain zoom levels. They were not rendered before.

There has not been any changed in place= rendering.

While some mappers add nodes to administrative boundary relations with role administrative_centre or label, this is not established practice, and this map style does not use that information in any way.