The style does not honor population_rank, and adding "symbol-sort-key": ["*", -1, ["get", "pmap:population_rank"]] to the places_locality layer's layout properties fixes the issue. However, better I think would be to sort the features in the tiles according to pmap:population_rank to avoid this issue.

We are using setSortKey already here:

The planetiler docs state:

For symbols (text/icons) where clients try to avoid label collisions, features are placed in the order they appear in each layer, so features that appear earlier (lower sort key) will show up at lower zoom levels than feature that appear later (higher sort key) in a layer.

l'Hospitalet de Llobregat:

id | 17593125925341
-- | --
name:ru | Оспиталет-де-Льобрегат
capital | 8
name:el | Οσπιταλέτ ντε Λιοβρεγάτ
name | l'Hospitalet de Llobregat
pmap:kind_detail | city
pmap:min_zoom | 8
pmap:kind | locality
pmap:pgf:name | l'Hospitalet de Llobregat
wikidata | Q15470
pmap:population_rank | 10
population | 274455

collides away the Barcelona label:

id | 17592338408581
-- | --
capital | 4
name:uk | Барселона
pmap:kind_detail | city
pmap:pgf:name:hi | 
name:el | Βαρκελώνη
name:it | Barcellona
pmap:min_zoom | 4
name:en | Barcelona
name:es | Barcelona
name:zh | 巴塞罗那
pmap:population_rank | 12
name:ar | برشلونة
name:ja | バルセロナ
name:pl | Barcelona
pmap:kind | locality
name:ro | Barcelona
name:tr | Barselona
population | 1660122
name:ru | Барселона
name:pt | Barcelona
name:de | Barcelona
name:hi | बार्सॆलोना
name:lt | Barselona
name | Barcelona
name:fr | Barcelone
name:zh-Hans | 巴塞罗那
name:zh-Hant | 巴塞隆納
pmap:pgf:name | Barcelona
wikidata | Q1492

getSortKey(4, 2, 12, 1660122, "Barcelona")
return -2647735

getSortKey(8, 2, 10, 274455, "l'Hospitalet de Llobregat")
returns -1207431

which looks correct.

com.onthegomap.planetiler.collection.FeatureGroup.SORT_KEY_MIN is -4194304 so there should not be an overflow

@wipfli what may be happening is although the sort order within a tile is correct, these two labels for l'Hospitalet de Llobregat and Barcelona actually come from different tiles:

A better screenshot:

Good observation. We can supply a sort key to MapLibre GL JS in that case.

Same issue in New York at z10.6:

https://maps.protomaps.com/#map=10.63/40.6567/-73.9021&theme=light&tiles=https://build.protomaps.com/20240824.pmtiles

And z4.4:

https://maps.protomaps.com/#map=4.41/36.4/-64.67&theme=light&tiles=https://build.protomaps.com/20240824.pmtiles

Any alternative to including a sort key in the tiles for MapLibre GL JS?

What is the tile buffer set to for the places layer?

The buffer size is 64 I think:

@msbarry have you experience previously that labels start to blink if the buffer size was set too low on a symbol layer?

I've always seen labels blinking on gl js, it tries to optimize labels on the current viewport but that leads to labels disappearing and reappearing when you zoom in or out 😕. 64px seems like plenty, I'm only using 4px on onthegomap. I'm not exactly sure how it handles label collisions preference across tiles based on ordering within each tile but it seems like specifying a global ordering should help, except that it might show a label when one tile loads but then need to hide it when adjacent one loads.

Seeing the same thing for Florence: https://maps.protomaps.com/#map=9.25/43.7929/11.0961&theme=light&lang=en

@nvkelso I think we should just add a sort_rank to all layers which will also aid Tilezen backwards-compatibility.

Here's the order of locality features in that tile (9/271/186). It matches what I'd expect based on this logic:

I'm looking at 3 labels that blink when you zoom in: Montale, Montemurlo, and Agliana. My hunch is that a large (and growing as you zoom in) value for text-padding is causing this.

When you're fully zoomed in there is space for all 3:

Then you zoom out some more and it correctly hides the least important one (Montale)

But then you zoom out a little further and since Montemurlo is too close and collides with Agliana, it gets hidden and there is now room for Montale

It would help if there were a way to set map.showCollisionBoxes=true in that style viewer.

That's only one source of blinking though, it's very strange that florence gets hidden sometimes even though it appears first in the 2 tiles it's on the border of. My guess with that one is that you need the sort key for maplibre to know how to handle collisions across neighboring tiles. Or we could go into the maplibre code and try to make it smarter about interleaving features when handling collisions across neighboring tiles.

Added a "boxes" option on maps.protomaps.com that shows tile boundaries and label bbox boundaries.

I propose pre-culling excess labels in tiles in #300. Once that's merged, the too large collision boxes can be trimmed down to more reasonable few pixels (needs a style PR), and the collision flicker should mostly be eliminated.