scale_size
scales area, scale_radius
scales radius. The size
aesthetic is most commonly used for points and text, and humans perceive
the area of points (not their radius), so this provides for optimal
perception. scale_size_area
ensures that a value of 0 is mapped
to a size of 0.
scale_radius(name = waiver(), breaks = waiver(), labels = waiver(),
limits = NULL, range = c(1, 6), trans = "identity",
guide = "legend")
scale_size(name = waiver(), breaks = waiver(), labels = waiver(),
limits = NULL, range = c(1, 6), trans = "identity",
guide = "legend")
scale_size_area(..., max_size = 6)
Arguments
name 
The name of the scale. Used as the axis or legend title. If
waiver() , the default, the name of the scale is taken from the first
mapping used for that aesthetic. If NULL , the legend title will be
omitted. 
breaks 
One of:
NULL for no breaks
waiver() for the default breaks computed by the
transformation object
A numeric vector of positions
A function that takes the limits as input and returns breaks
as output

labels 
One of:
NULL for no labels
waiver() for the default labels computed by the
transformation object
A character vector giving labels (must be same length as breaks )
A function that takes the breaks as input and returns labels
as output

limits 
A numeric vector of length two providing limits of the scale.
Use NA to refer to the existing minimum or maximum. 
range 
a numeric vector of length 2 that specifies the minimum and
maximum size of the plotting symbol after transformation. 
trans 
Either the name of a transformation object, or the
object itself. Builtin transformations include "asn", "atanh",
"boxcox", "exp", "identity", "log", "log10", "log1p", "log2",
"logit", "probability", "probit", "reciprocal", "reverse" and "sqrt".
A transformation object bundles together a transform, its inverse,
and methods for generating breaks and labels. Transformation objects
are defined in the scales package, and are called name_trans , e.g.
scales::boxcox_trans() . You can create your own
transformation with scales::trans_new() . 
guide 
A function used to create a guide or its name. See
guides() for more info. 
... 
Arguments passed on to continuous_scale
 name
The name of the scale. Used as the axis or legend title. If
waiver() , the default, the name of the scale is taken from the first
mapping used for that aesthetic. If NULL , the legend title will be
omitted.
 breaks
One of:
NULL for no breaks
waiver() for the default breaks computed by the
transformation object
A numeric vector of positions
A function that takes the limits as input and returns breaks
as output
 minor_breaks
One of:
NULL for no minor breaks
waiver() for the default breaks (one minor break between
each major break)
A numeric vector of positions
A function that given the limits returns a vector of minor breaks.
 labels
One of:
NULL for no labels
waiver() for the default labels computed by the
transformation object
A character vector giving labels (must be same length as breaks )
A function that takes the breaks as input and returns labels
as output
 limits
A numeric vector of length two providing limits of the scale.
Use NA to refer to the existing minimum or maximum.
 oob
Function that handles limits outside of the scale limits
(out of bounds). The default replaces out of bounds values with NA .
 na.value
Missing values will be replaced with this value.
 trans
Either the name of a transformation object, or the
object itself. Builtin transformations include "asn", "atanh",
"boxcox", "exp", "identity", "log", "log10", "log1p", "log2",
"logit", "probability", "probit", "reciprocal", "reverse" and "sqrt".
A transformation object bundles together a transform, its inverse,
and methods for generating breaks and labels. Transformation objects
are defined in the scales package, and are called name_trans , e.g.
scales::boxcox_trans() . You can create your own
transformation with scales::trans_new() .
 guide
A function used to create a guide or its name. See
guides() for more info.
 position
The position of the axis. "left" or "right" for vertical
scales, "top" or "bottom" for horizontal scales
 super
The super class to use for the constructed scale
 expand
Vector of range expansion constants used to add some
padding around the data, to ensure that they are placed some distance
away from the axes. Use the convenience function expand_scale()
to generate the values for the expand argument. The defaults are to
expand the scale by 5% on each side for continuous variables, and by
0.6 units on each side for discrete variables.

max_size 
Size of largest points. 
See also
scale_size_area()
if you want 0 values to be mapped
to points with size 0.
Examples
p + scale_size("Highway mpg")
# If you want zero value to have zero size, use scale_size_area:
p + scale_size_area()
# If you want to map size to radius (usually bad idea), use scale_radius
p + scale_radius()