Default 'bin-linear' scale for binned size and opacity channels. Note:
Symbols use discretized opacity here so why doesn't the legend feature
opacity?
Default 'bin-ordinal' scale for discretized legend
Quantile scale. Legend categories should be <43, 43-53, 53-81 and
>=81.
Quantize scale. Legend categories should be <37, 37-55, 55-73 and
>=73.
Threshold scale. Legend categories should be <30, 30-70 and >=70.
Default size scaling
Size scaled by with exponent of 2 (by square of radius)
Size scaled with flannery perceptual scaling (exponent of 1.2).
Log to base e scale