title: R levelplot adjust colour scale
body: <p>I am trying to adjust my colour scale on a level plot using the rasterVis package. My code plots a raster. I am using manually set colour scale that classifies that data into 5 quantiles. I would like to have the labels stay at the values I have set, but instead of a linear scale as it appears now, have equal space between the labels. Is this possible with levelplot??</p>
  
  <pre><code>cor = M[, c("lon", "lat")]
  sPDF &lt;- SpatialPointsDataFrame (cor, data=M)
  proj4string(sPDF)&lt;-(p$geog.proj)
  
  #Create Rasters
  grid.sum &lt;- rasterize(x=sPDF, y=grid, field=v, fun=grid.fun)
  
  #Define colour scale
  z &lt;- getValues(grid.sum)
  z &lt;- z[is.finite(z)]
  z &lt;- round(z, digits=0)
  
  quant &lt;- unique(quantile(z, seq(0,1, length.out=75)))
  quant.small &lt;- unique(quantile(z, seq(0,1, length.out=5)))
  ckey &lt;- list(at=quant, labels=list(at=quant.small))
  
  
  print(
    levelplot(grid.sum, at=quant, colorkey=ckey, col.regions=p$seis, 
      alpha.regions=1, margin=F, xlab="", ylab="", main=name, 
      scales = list(x=list(cex=0.7), y=list(cex=0.7)))
      + layer(sp.polygons(coast, fill='lightgrey', alpha = 0.2))
      + layer(sp.lines(contours, col='dimgrey', alpha=0.6, lwd= 0.4)))
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/6zGOM.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/6zGOM.jpg" alt="enter image description here"></a></p>