I am trying to add a list of exponential symbols for a legend entry that is not displaying as I expected in the print layout. For context, I have a list of earthquakes with magnitudes and I want to plot those event locations with a circle symbol who's size grows exponentially with it's magnitude, giving extra emphasis to large earthquakes. I am using version QGIS 3.16 for my example below.
In the symbology tab of the layer properties, I initially used the graduated symbol style which worked, but I was only ever able to get the scaling to be linear, so lower magnitude events obscured the larger events. I found this page on the stack exchange (Changing symbol size using the "Size assistant" in QGIS?) that showed and example of how to create the desired effect with the single symbol (instead of graduate) method, so I followed the example there and edit the size using the size assistant.
I could then manually control where the exponential size of the symbols increased and by what factor. This window shows how I scaled the symbols based on their Magnitude attribute.
The trouble I am having is that when I try and display this symbol in the legend of the print layout, only a single entry for the Magnitude is shown. This makes sense as I switched from a "graduated" symbology to a single symbol style.
Is there a way for me to show a similar scale shown in the Symbology assistant in the print layout legend? Is there a way to create this exponential growth symbology in the Graduated Symbol class instead? When I examined options with using a graduated symbol, I couldn't find a mode available to scale the symbols on an exponential scale.
The page I highlighted at the beginning even has a comment about a legend issue, but no link or follow up comment was ever provided.