title: alpha value in geom_point {ggplot2}
body: <p><code>ggplot2::geom_point</code> <a href="http://docs.ggplot2.org/current/geom_point.html" rel="nofollow">documentation</a> notes that <em>varying alpha is useful for large datasets</em>. The below snippet generates two plots for two alpha values:<br></p>
  
  <pre><code>library(ggplot2)
  data("diamonds")
  d &lt;- ggplot(diamonds, aes(carat, price))
  d + geom_point(alpha = 1/10) # alpha = 1/10
  d + geom_point(alpha = 1/20) # alpha = 1/20
  </code></pre>
  
  <p>How would one interpret the value of <code>alpha</code>? As the plots can be easily produced with the above snippet, I did not provide the plots (can provide should it be necessary).</p>