Explicit layer ordering?

[gravitystorm]

When I design styles in CartoCSS, I tend to have separate files for each "theme", e.g. roads.mss, water.mss, landcover.mss and so on. These are then included in the main style file. However, each of the theme files contains a mixture of polygon, point, text and icons definitions. Therefore I rely on the explicit layers attribute in project.yml to control the draw ordering, e.g. all polygons from every theme, before any text.

An alternative approach is to split the themes into individual glug files for each layer, and then include them in the desired order, e.g.

include_file 'landcover_polygons'
include_file 'water_polygons'
include_file 'roads_polygons'
include_file 'water_lines'
...
include_file 'water_point_labels'
include_file 'water_line_labels'

This would work, but leads to a bit of an explosion in the number of files required! It splits each theme into multiple files, maybe 3-4 per theme.

My idea would be to just have an array of layer ids, and then after the rest of the stylesheet has been evaluated, the generated layers are filtered and sorted by the contents of that array.

My question, for people who have more experience than I do with glug, is whether an explict "layers" definition would be useful, or whether that's just excessive complexity?

[pnorman]

This has been an issue for me too.

You don't need to go all the way as having a file per layer, e.g. most thematic categories have two files in my styles. One for paints, one for labels.

I'm not sure of a good solution

[systemed]

I could imagine an optional sort_order parameter in the layer definition. Then before the layers are written, they’re sorted by .sort_order (if present).