title: Increase breaks in discrete legend
body: <p>I'm currently getting started learning R and I'm focusing on data visualisation.</p>
  <p>For this plot, I'm displaying the count of overlapping dots on the map using geom_count which gives me the following graph</p>
  <p><img src="https://i.stack.imgur.com/tvG3Y.jpg" alt="geom_count graph with only 2 legend elements" /></p>
  <p>As you can see the legend only contains two elements, namely the size of the dot when 5 data points are overlapping, and the size of it when 10 data points are overlapping. How can I increase the breaks that the legend includes? I have been trying with to use discrete_x_scale in order to increase the number of breaks but I just get lost and can't manage it.</p>
  <p>The code for my current graph is simply this</p>
  <pre><code>ggplot(data = mpg, mapping = aes(x = cty, y = hwy)) + 
    geom_count()
  </code></pre>
  <p>I would also like to know how to change the filling color of the dot according to the number of overlapping data points.</p>