title: How do I map a variable to aes fill in geom_point?
body: <p>Conceptually I thought a point would be dimensionless but I saw in the documentation that <code>geom_point</code> actually takes the aesthetic <code>fill</code>. However it doesn't seem to work for me:</p>
  
  <pre><code>ggplot(data = mtcars) + geom_point(aes(mpg, disp, fill = carb))
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/0KzvN.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/0KzvN.png" alt="enter image description here"></a></p>
  
  <p>The aesthetics seems to be ignored, by I would expect a warning similarly to <code>geom_line</code>:</p>
  
  <pre><code>ggplot(data = mtcars) + geom_line(aes(mpg, disp, fill = carb))
  </code></pre>
  
  <blockquote>
    <p>Warning: Ignoring unknown aesthetics: fill</p>
  </blockquote>