Performance with multiple layers vs. multiple files

[avida01]

Hello everyone,

I'm working on a project using MapLibre GL JS with PMTiles to visualize oceanographic/meteorological data. The data is converted from NetCDF to GeoJSON and then to PMTiles using Tippecanoe. My project involves a unique PMTiles file that contains 24 layers, one for each hour. My goal is to allow the user to switch dynamically between these hours, displaying only ONE layer at a time using the source-layer property.

I'm running into a performance question and I'm not sure if my approach is the most efficient. I have a feeling that even when I'm only displaying a single layer, MapLibre is downloading or at least processing data for all 24 layers.

My main question is:
Am I truly taking advantage of PMTiles' byte-range requests if I'm combining all 24 hours into a single file?

Based on my understanding, a PMTiles client (like MapLibre) requests a specific tile (z/x/y). If that tile contains all 24 layers, wouldn't the browser download the entire tile payload, even if I'm only using one source-layer in my map style?

I'm considering an alternative where I generate 24 separate PMTiles files, one for each hour. My app would then dynamically change the url of the source instead of just the source-layer.

Could someone from the community or the Protomaps team confirm if my initial approach is inefficient and if the separate-file approach is the recommended best practice for this use case?

Any insight would be greatly appreciated!

Thanks in advance.

[wipfli]

Tiles are the smallest unit of data that MapLibre fetches. So if your tiles have 24 layers, and maplibre needs one of these layer, maplibre will fetch the entire tile.

[avida01]

Hi @wipfli , thank you for the clarification, it confirms 100% that my original strategy was incorrect.

I tested your suggestion by taking a single band from the NetCDF file and generating a dedicated PMTiles file for it. The result was a significant decrease in the network request size and a noticeable increase in the loading speed, which fully validates your point.