title: ggplot2 legend with only one category / with only the shape and no scale
body: <p>How can I have a section of the legend with only one category? I tried to mess with the <code>override.aes</code> without sucess. Alternatively, the desired output could be seen as a legend with only the shape but not the scale.</p>
  
  <pre><code>ggplot(iris) +
    geom_point(aes(x=Sepal.Width, y=Sepal.Length, color=Species, size=Sepal.Length))+
    scale_size_continuous("Legend with \n only 1 circle ",range = c(5,10))+
    guides(size = guide_legend( override.aes=list(range=  c(1,5)))) 
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/4LdCM.png" rel="noreferrer"><img src="https://i.stack.imgur.com/4LdCM.png" alt="image1"></a></p>
  
  <p>An illustration of the type of <a href="http://www.scmp.com/news/china/diplomacy-defence/article/1887975/infographic-chinas-total-investment-africa" rel="noreferrer">product</a> I am trying to get to:<a href="https://i.stack.imgur.com/eUDQy.png" rel="noreferrer"><img src="https://i.stack.imgur.com/eUDQy.png" alt="map2"></a></p>
  
  <p>Points are scaled but the legend does not report the scale.</p>