@mbostock could we rename `r` to `circleRadius`? It'd be much clearer for folks already holding a lot of new information! Thanks!

What is 'DOM'? I just copied the above code into my project and it shows: ' DOM ' is not defined

DOM is documented here https://observablehq.com/documentation/misc/standard-library#dom it is a convenient way to create a canvas, but you can substitute d3.create("canvas").attr("width", width).attr("height", height) if you prefer (or 2 * width, 2 * height if you want high-density images).