title: Reducing line thickness / size in multiple qplot graphs in R
body: <p>I wish to create 24 line plots on an A4 page in a high resolution png. I'm trying to do this using qplot and the grid.arrange function in the gridExtra library. My problem is that I can't reduce the thickness of the lines in each plot, below a certain threshold. Setting size=0 or size=0.0001 or whatever makes no difference; there seems to be a minimum that can't be crossed, and it's much thicker than I'd like. Increasing the size of the plot area works but then I have to rescale the resulting image. Can anyone please suggest an alternative? A minimal example is below.</p>
  
  <pre><code>library(ggplot2)    
  library(gplots)
  library(gridExtra)
  
  a &lt;- c(0,1,2,3,4,5)
  b &lt;- a^2
  
  plot1 &lt;- qplot(a, b, geom = c("point", "line"), pch=10) + 
               geom_point(size=0) + 
               geom_line(size=0)
  png("filename.png", width=15, height=22, units = "cm", res = 900)
  
  grid.arrange(
  plot1,plot1,plot1,plot1,
  plot1,plot1,plot1,plot1,
  plot1,plot1,plot1,plot1,
  plot1,plot1,plot1,plot1,
  plot1,plot1,plot1,plot1,
  plot1,plot1,plot1,plot1,
  ncol=4)
  
  dev.off()
  </code></pre>