Alpha-transparency scales are not tremendously useful, but can be a convenient way to visually down-weight less important observations. scale_alpha is an alias for scale_alpha_continuous since that is the most common use of alpha, and it saves a bit of typing.

scale_alpha(..., range = c(0.1, 1))

scale_alpha_continuous(..., range = c(0.1, 1))

scale_alpha_discrete(..., range = c(0.1, 1))



Other arguments passed on to continuous_scale or discrete_scale as appropriate, to control name, limits, breaks, labels and so forth.


Output range of alpha values. Must lie between 0 and 1.

See also

Other colour scales: scale_colour_brewer, scale_colour_gradient, scale_colour_grey, scale_colour_hue


p <- ggplot(mpg, aes(displ, hwy)) + geom_point(aes(alpha = year)) p
p + scale_alpha("cylinders")
p + scale_alpha(range = c(0.4, 0.8))