title: How to background geom_vline and geom_hline in ggplot 2 in a bubble chart
body: <p>I would like to add a vertical line and a horizontal one on a bubble chart, without overplotting the bubbles. Here come the data:</p>
  
  <pre><code>a&lt;-c("np", "prepp", "vp", "animal", "artifact", "communication", "ipv", "isv")
  b&lt;-c(-0.51, 0.32, 0.85, -0.61, -0.36, 0.86, -0.02, 1.05)
  c&lt;-c(0.10, 0.25, -0.20, 0.99, 1.09, -0.35, 0.00, -0.08)
  d&lt;-c(68.23, 4.87, 41.42, 2.44, 19.49, 2.44, 112.09, 2.44)
  e&lt;-c("synt", "synt", "synt", "sem", "sem", "sem", "cx", "cx")
  
  data&lt;-cbind(a, b, c, d, e)
  colnames(data)&lt;-c("Variables", "Dim.1", "Dim.2", "Freq_pmw", "SynSem_index")
  data&lt;-as.data.frame(data)
  data[, 2]&lt;-as.numeric(as.character(data[, 2]))
  data[, 3]&lt;-as.numeric(as.character(data[, 3]))
  data[, 4]&lt;-as.numeric(as.character(data[, 4]))
  
  radius&lt;-sqrt(data$Freq_pmw/pi)
  
  plot&lt;-ggplot(data, aes(x=data$Dim.1, y=data$Dim.2)) + 
    xlim(-1, 1.5) + ylim(-1, 3) + 
    theme_bw() + xlab("Dimension 1") + ylab("Dimension 2")
  plot&lt;-plot+geom_point(aes(size=radius, col="darkgrey", fill=data$SynSem_index), pch=21, show.legend=F)+
    scale_size_continuous(range=c(1, 20)) +
    geom_text_repel(label=data$Variables, size=3) +
    geom_vline(colour="red", xintercept=0) +
    geom_hline(colour="red", yintercept=0)
  plot
  </code></pre>
  
  <p>The output of this is rendered with the following graph:</p>
  
  <p><a href="https://i.stack.imgur.com/OLP94.png" rel="noreferrer"><img src="https://i.stack.imgur.com/OLP94.png" alt="enter image description here"></a></p>
  
  <p>How to avoid overplotting the bubbles with the coordinate axes?</p>
  
  <p>Thanking you in advance!</p>