Zoom level transparency changes are creating undesirable effects

[jeffreyameyer]

Bug description What is happening? When I look at where I've imported some natural=wood over a large area at different zooms, there are some very different effects going on across the areas of natural=wood.

See Glacier National Park:

At zoom=11, the coloring in the natural=wood areas is consistent.

At zoom=10, the coloration is very inconsistent, often along blocky boundaries. I'm wondering if this is a weird artifact of our terrain layer, but I would think that would be under our data.

Here's zoom=9:

same for zoom=8:

What should be happening? These areas should all be consistent in appearance and not blotchy.

[jeffreyameyer]

Ok.... this may be a problem in the underlying import data... and also in something we're doing in our rendering.

The vtiles reflect the same shading differences:

So, it looks like some sort of transparency is being applied to the fills as you zoom out, creating the different intensities, but is that the correct behavior? Shouldn't it be a constant alpha? Otherwise, in areas where we have overlapping landcover, but 1 is supposed to be "over" the other, the areas of overlap won't be visible at higher zooms (good), but will be at lower zooms (bad).

[jeffreyameyer]

What's weird to me is that the transparency effects disappear at zoom=7 and zoom=6 - see below:

[vknoppkewetzel]

I do not see this happening on my end (copy pasting your image): I only see the below on my end:

I DO see that there are 3 different landuse data layers. One for z5, one for z7, and one for z10, and then broader diversity in z12.

Taking a look at these and will make some changes, at least for the consistency in zoom in/out using the above as example

[vknoppkewetzel]

Made some updates and reviewed across zoom levels, lmk what you think. Demo style: https://openhistoricalmap.github.io/mbgl-timeslider/demo/#3.309/34.68647/-96.42187/2023,-4000-2023

[vknoppkewetzel]

in style ✅