title: cex equivalent in ggplot2
body: <p>In my work, I frequently display scatterplots using text labels. That's meant a <code>plot()</code> command, followed by <code>text()</code>. I used <code>cex</code> to adjust to font size to what I wanted it very quickly.</p>
  <p>I created a text scatterplot very quickly using <code>qplot</code>. But I can't adjust the size fast. Here's a silly code example:</p>
  <pre><code>data(state)
  qplot(Income, Population, 
    data=as.data.frame(state.x77), 
    geom=c(&quot;smooth&quot;, &quot;text&quot;), method=&quot;lm&quot;, 
    label=state.abb)
  </code></pre>
  <p>Whereas in the old days I'd do:</p>
  <pre><code>plot(xlim=range(Income), ylim=range(Population),
    data=state.x77, type=&quot;n&quot;)
  text(Income, Population, state.abb, 
       data=state.x77, cex=.5)
  </code></pre>
  <p>If I wanted the text size halved from what I saw at the defaults (oh, and I'd have to do a linear regression manually and add <code>abline()</code> to get the regression line -- nice to do it all in one via ggplot2).</p>
  <p>I know I can add a size adjustment with size, but it's not a relative size adjustment like I'm used to. Hadley tweeted me to say that size is measured in mm, which isn't fully intuitive to me. Since I often adjust the size of the plot, either in R or in LaTeX, an absolute scale isn't as useful to me.</p>
  <p>I must be missing something really simple. What is it?</p>