when adding a layer from a wms, discovered via cssw-catalog, all layers are added at once

[pvgenuchten]

I'm trying to find out what happens, so let me describe how I reproduce the issue

At https://rwanda.lsc-hubs.org/map/ we host a recent version of Terria, When opening the CSW catalog in explore data and search for 'slope'

Then click + button on any layer

Expected: Single layer is added to map

Instead: All layers of that WMS are requested in a single map request, causing slow response/heavy server load and a large numbers of legends being displayed

The challenge is that the metadata does not (properly) identify which of the layers in the WMS are the relevant one, so terria decides to add all of them, this aspect is also mentioned in #6866, in stead suggestion could be to add the top 5 layers only? Or alternatively, move the + button to a select layer section in:

[zoran995]

Hi @pvgenuchten, it might be a better approach to have the possibility to specify the handling of wms layers as wms-group or wms that way it would you would just specify the proper value and catalog and have the layers as a wms-group. I have posted the same idea as the comment on #6866 so let's see first what Nick thinks about it and if it is even possible