title: Set the scale in ggplot to be 1:1 in r
body: <p>I would like to set the x and y axis in the following plot to have the same scale distance (i.e. 0.1 on the x axis is the same length as 0.1 on the y axis). Any advice? Thanks.</p>
  
  <pre><code>df &lt;-data.frame(x = c(0,0.2,0.5), y = c(0.6,0.7,0.9))
  
  p &lt;-ggplot(df, aes(x, y, ymin=0, ymax=1, xmin=0, xmax=1))
  
  p &lt;- p + geom_point(alpha=2/10, shape=21, fill="blue", colour="black", size=5)
  
  grid.arrange(p, p,ncol=1)
  
  p
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/xSddA.png" alt="enter image description here"></p>