Isn't it the case that pre-rendered tiles are more performant for the mobile user? Continously rendering the tiles on a smartphone is draining more battery? I would guess?
It's true that raster tiles are easier to draw, but CPU/GPU is rarely the limit for performance even on (modern) mobile devices, network access then disk access then memory usage is. And using the network is one of the largest sources of power use. Vector tiles are smaller downloads, therefore they are more performant.
Wall time CPU profiling is just not that useful anymore and yet it's the only thing most people ever think about for some reason.
Along with dynamic rendering mentioned in other comments, vector data is sparse, so bandwidth is basically zero past a certain (surprisingly low) zoom. Raster tiles are a dense data structure, so you need to bake tiles to the maximum allowed zoom and clients need to download them. High zoom tiles also have higher entropy so you end up with a huge volume of images with low cache hit rates. It’s expensive for the provider and slow for bandwidth constrained mobile users.
Yeah, pre-rendered tiles are typically more performant on any device. It’s basically downloading and displaying a png. In my experience, download times were not the bottleneck for vector tiles, but rather all the on-device rendering. This is especially true when you consider that most of the time, the tiles are already cached on your device.
I believe the reason most companies moved to vector had more to do with the other stuff gp mentioned: ability to rotate, dynamically show/hide features, etc.
If you never change what you display, that might well end up being true, but if changing display state (you want to highlight or shade or hide a feature, for example) that would likely require downloading whole new tiles for raster but could be a pretty trivial mutation of the current local state that doesn't require a full re-render from scratch. You probably also don't need to download as much on zoom; there are tiles for different zoom levels with vector tiles because tiles get really large when zoomed way out otherwise, mostly full of features or detail you can't see or wouldn't show, but you might not need as many, and can overzoom a given tile and have it still look nice with relatively few artifacts. All of which is to say: it depends.
To some degree its possible to combine bitmap tiles and client side lightweight vector overlay. If you want to work with ortofoto (basically satellite/airplane captured imagery) then you basically have to do it that way.
Definitely true. In my experience it's less to do with battery and more that the client-side rendering process is so intense. Particularly because of the single-threaded nature of JS: a GL-based map on a web page makes the whole thing drag on a low-specced phone.
These days Chrome and Firefox have the OffscreenCanvas API that would let you do all that rendering in a different thread, but last I looked MapBox GL didn't support it. Not sure if that's changed with libre.
