Proportional symbol mark?

[Fil]

Speaking in general, we have several possibilities for proportional symbols:

• svg:circle is concise (and possibly the most cpu-efficient); scale with r/size.
• svg:path + d3.symbol is useful for certain types of scatterplots, but difficult to extend; scale with transform:scale
• svg:text + emoji works if we're careful to center the mark properly; scale with transform:scale

Note that svg:use + defs covers the three cases, and removes the difficulty of having to define complex symbols when we're not happy with the set in d3.symbols.
See https://observablehq.com/@fil/svg-use

So if we want a variant of Plot.dot that allows various symbols, I would try to code it with <use>. The range of the symbol scale is a list of objects that would have an id and be added to the defs, or a list of ids—but then how do we pass the objects themselves? The mark could default to <use href=#square>. And it would accept an orientation channel!

(discarding svg:polygon which has no advantage that I know of over svg:path.)

[Fil]

An experiment here: https://observablehq.com/@fil/plot-symbols

[Fil]

Linked to #170

[Fil]

See also the preattentive symbols by Heman Robinson https://observablehq.com/@heman/preattentive-symbols-176

[mbostock]

Fixed in #652 #649.