title: Reverse and change limit of axis
body: <p>I am trying to create a contour plot. I would like to have depth on the Y-axis and time on the X-axis. Right now this is the code that I am using:</p>
  
  <pre><code>par &lt;- ggplot(up_PAR, aes(Time.hour.of.the.day., Depth, z = PAR))
  parplot &lt;- par + 
             stat_contour(bins=20, aes(colour=..level..))+ 
             scale_colour_gradient(limits=c(0.000842, 0.00000000195),low="black", high="black") +
             scale_y_reverse()+
             theme_bw()+
             theme(panel.grid.major = element_blank(), panel.grid.minor = element_blank())+
             xlab("Hour of the Day")+
             ylab("Depth(m)")+
             ggtitle("Downwelling PAR (photons/m2/s), January 22nd")
  direct.label(parplot)
  </code></pre>
  
  <p>However, I would like to extend the Depth axis to span from 0-30m. My dataset goes to 175m, but I am only interested in showing the top of the water column.</p>
  
  <p>I know that I can use <code>scale_y_continuous(limit=c(0,30))</code> but since I've already reversed my axis, and would like to keep it that way, I am unable to also set the limits of the axis.</p>