Concurrent shields overlap at either end of divided highway

[1ec5]

Shields in a route concurrency overlap each other wherever the road transitions from being undivided to being divided (dual carriageway).

Zooming in, it’s apparent that this is caused by one-way LineString features getting merged together despite going in opposite directions.

While this merging isn’t ideal, there’s a straightforward workaround at the style level. Currently, the highway shield layer specifies a text-max-angle of 180 degrees, which is enough to allow the label to double back on itself. We give road name labels a much less generous text-max-angle of 20 degrees. I think a similar value should be applied to the highway shield layer for consistency.

openstreetmap-americana/src/layer/highway_shield.js

Line 60 in 0a0c9fa

"text-max-angle": 180,

openstreetmap-americana/src/layer/road_label.js

Line 8 in 0a0c9fa

"text-max-angle": 20,

[jleedev]

It's actually four separate lines in the tile. Does the frontend merge these? Never mind, I'm not looking at transportation_name here.

[1ec5]

It's actually four separate lines in the tile. Does the frontend merge these? Never mind, I'm not looking at transportation_name here.

Hm, you do have a point though. GL JS doesn’t merge linestrings in general, but it does merge them for the purpose of label placement, as long as the text-field is equivalent. (Not even icon-image keeps them from merging: mapbox/mapbox-gl-js#3645.) Regardless, I think a smaller text-max-angle would prevent the label from doubling back on itself, even if it’s a single feature in OSM.