title: R geom_tile ggplot2 what kind of stat is applied?
body: <p>I used <code>geom_tile()</code> for plot 3 variables on the same graph... with </p>
  
  <pre><code>tile_ruined_coop&lt;-ggplot(data=df.1[sel1,])+
    geom_tile(aes(x=bonus, y=malus, fill=rf/300))+
    scale_fill_gradient(name="vr")+
    facet_grid(Seuil_out_coop_i ~ nb_coop_init)
  tile_ruined_coop
  </code></pre>
  
  <p>and I am pleased with the result !</p>
  
  <p><img src="https://i.stack.imgur.com/PQkLo.png" alt="ggplot2 geom_tile exemple"></p>
  
  <p>But What kind of statistical treatment is applied to <code>fill</code> ? Is this a mean ? </p>