When using web map services such as Leaflet/Openlayers etc, are different raster layers fetched separately and laid on top of each other client-side, or are they composed on the server side?
Thank you
It depends if you make a separate request for each layer then the server will generate one image for each layer. However, if you make a request with several layers in it then the server will send back one combined image for all the layers, this is usually fastest.