Plot should be able to show the dot size scale in a legend

[llimllib]

As far as I can tell, if you use the r scale in a dot plot, there is no way to give the reader of the plot any indication of what the radius represents.

• Is that accurate? I don't see any examples of a legend for dot size
• If so, plot should have a way to easily tell the reader what is being represented with

Having the r channel available by default, but not label-able by default (if that is indeed the case!) is likely to make it confusing unless the chart's author goes well out of their way to provide a label.

I made a simple demonstration of what I mean here

How should it look?

I don't honestly know, this is an area for research! A graph tool I wrote in d3 uses a circle mark:

But honestly I'm not super happy with how well that conveys the information, and many people here are vastly better at visual design than myself. I suppose I should go take a look in the semiology of graphics for ideas, but I'm not at home so I can't look right now.

[llimllib]

Vega-lite puts a legend to the side

[llimllib]

ggplot also puts a legend to the side

[llimllib]

Oh! It appears to be considered but stalled. Consider this a request for the feature. I don't as much care what exactly the legend looks like as that I can convey to my viewers what the values mean at all!

[Fil]

Yes it's a bit stalled, thanks for voting it up :)

In the meantime a solution is to name your chart, then use chart.scale("r") to draw your own, with Plot, D3, or even in raw SVG.

[llimllib]

I don't have any practical idea what that means, but I'll cross that bridge when I get to it. Thanks for the update

[Fil]

This notebook shows a way to use the code from the PR:
https://observablehq.com/@recifs/a-radius-legend-for-plot-665