title: How to increase the size of points in legend of ggplot2?
body: <p>I have thousands of points in one figure and set <code>size = 1</code>. However, the point size in the legend is reduced too. How to increase the point size in the legend?</p>
  <p>For example.</p>
  <pre><code>num &lt;- 10000
  set.seed(1)
  df &lt;- data.frame(x = seq(1, num), y = runif(num), z = rep(1:2, each = num / 2))
  df$z &lt;- factor(df$z)
  library(ggplot2)
  p &lt;- ggplot(df, aes(x, y, colour = z)) + geom_point(size = 1)
  p
  </code></pre>
  <p><img src="https://i.stack.imgur.com/1W6GX.png" alt="The size of points in legend" /></p>