How to retain text symbols on MultiLineString at lower zoom

[tshropshire]

mapbox-gl-js version: v2.14.1

Question

Here is a gif showing the issue

I have generated contour lines from topographic data which is in the form of GeoJSON MultiLineStrings. I upload and create a vector tile using Tilesets CLI and add the source and layer to a map using Mapbox GL JS. The issue I am having is that the contour line labels (which are read from the MultiLineString attribute "title") are disappearing as I zoom out far before my prescribed minzoom value. The minzoom value is specified in the tileset recipe and when adding the layer to a map. I have found that if I use "symbol-placement: "point" rather than "line" the labels appear at the correct zoom, albeit not distributed multiple times along the line. Appreciate any suggestions!

I have played around with "text-allow-overlap", "symbol-spacing", "text-justify" and others with no luck.

Here is my recipe

{ "version": 1, "layers": { "bathy_cont_layer": { "source": "mapbox://tileset-source/USRE_PLACEHOLDER/TILESET_PLACEHOLDER", "minzoom": 5, "maxzoom": 12, "features": { "simplification": { "distance": 0 } } } } }

Here is how the source and layer are added

map.addSource('bathy_cont_source', {
type: 'vector',
url: 'mapbox://USER_PLACEHOLDER.TILESET_PLACEHOLDER'
});

map.addLayer({
'id': 'bathy_cont_line',
'type': 'line',
'source': 'bathy_cont_source',
'source-layer': 'bathy_cont_layer',
'layout': {
'visibility': 'visible',
},
'paint': {
'line-color': '#000000',
'line-width': ['interpolate',['linear'],['zoom'],7,2,10,3],
}
});

Here is how the contour line labels are added

map.addLayer({
'id': 'bathy_cont_text',
'type': 'symbol',
'source': 'bathy_cont_source',
'source-layer': 'bathy_cont_layer',
'minzoom': 5,
'maxzoom': 12,
'layout': {
'text-field': ['get','title'],
'symbol-placement': 'line',
'text-size': ['interpolate',['linear'],['zoom'],5,10,12,14],
'symbol-spacing':['interpolate',['linear'],['zoom'],5,100,12,10],
'text-font': ['Open Sans Semibold', 'Arial Unicode MS Bold'],
'icon-allow-overlap': true,
'text-allow-overlap': true,
'icon-ignore-placement': true,
'text-ignore-placement': true,
'text-justify': 'auto',
'visibility': 'visible'
},
'paint': {
'text-color': '#FFFFFF',
'text-halo-color': '#000000',
'text-halo-width': 2
}
});

Thanks again for any suggestions!

Links to related documentation

Here are two pages that I referenced in addition to digging through many forums.

https://docs.mapbox.com/help/troubleshooting/optimize-map-label-placement/
https://docs.mapbox.com/style-spec/reference/layers/#symbol