title: ggplot2 geom_point legend when size is mapped to a variable
body: <p>I am creating a plot in which the size of points is proportional to the values of a given variable, which I then square to increase the difference in sizes between points...</p>
  
  <pre><code># Using example from https://www3.nd.edu/~steve/computing_with_data/11_geom_examples/ggplot_examples.html #
  
  library(ggplot2)
  str(mtcars)
  
  p &lt;- ggplot(data = mtcars, aes(x = wt, mpg))
  p + geom_point(aes(size = (qsec^2)))
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/kxG7Q.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/kxG7Q.png" alt="enter image description here"></a></p>
  
  <p>From the resulting plot, is there a way to specify the size of the points which are shown in the legend and change the legend labels in order to reflect the original values and not the square of these values? (As edited by hand on the plot)</p>