title: ggplot2 geom_rug() produces different line length with wide plot
body: <p>I posted this as follow up to a 'sibling' question with lattice (i.e. <a href="https://stackoverflow.com/questions/33222841/lattices-panel-rug-and-ggplots-geom-rug-line-length#33223071">Lattice&#39;s `panel.rug` produces different line length with wide plot</a>) but due to different graphical system it deserves to be separate. </p>
  
  <p>When producing a wide plot in ggplot2 with margins that include <code>geom_rug()</code> from <code>ggthemes</code>, the length of the lines in rugged margins is longer in the y-axis than x-axis:</p>
  
  <pre><code>library(ggplot2)
  library(ggthemes)
  png(width=800, height=400)
  ggplot(swiss, aes(Education, Fertility)) + geom_point() + geom_rug()
  dev.off()
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/GMsL7.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/GMsL7.png" alt="enter image description here"></a></p>
  
  <p>I would like those <em>rug</em> lines in x- and y-axes to be the same length regardless of the shape of a plot (note: right now the <em>rug</em> lines will only be the same length when the plot is square).</p>