title: How to scale the size of line and point separately in ggplot2
body: <p>The code is as follows:</p>
  
  <pre><code>set.seed(123)
  d1=data.frame(x=runif(10),y=runif(10),z=runif(10,1,10))
  d2=data.frame(x=runif(10),y=runif(10),z=runif(10,100,1000))
  ggplot()+geom_point(aes(x,y,size=z),data=d1)+
  geom_line(aes(x,y,size=z),data=d2)
  </code></pre>
  
  <p>And the result is like this:</p>
  
  <p><a href="https://i.stack.imgur.com/np6N9.png" rel="noreferrer"><img src="https://i.stack.imgur.com/np6N9.png" alt="enter image description here"></a></p>
  
  <p>The size of points are too small so I want to change its size by <code>scale_size</code>. However, it seems both lines and points are influenced. So I wonder if there is a way to scale lines and points separately with a separate legend?</p>