title: distill colors of polygons on a map with ggplot2
body: <p>I'm trying to plot the different ways to name a pencil in France on a map with ggplot2. For each of the 96 departments of France, I have one item and a score associated to this item. I have no problem plotting the items according to their departments on a map, but I can't figure out a way to make the colors of each polygons vary according to their associated score. My data is <a href="https://www.dropbox.com/sh/2645g146q9bmeme/AABIif8cj5V1Wo1TAJxxZ7JKa?dl=0" rel="nofollow noreferrer">here</a>. The code to produce the map is below: </p>
  
  <pre><code>library(ggplot2)
  library(scales)
  library(Cairo)
  
  #open data
  plotDatafr = read.table("plotDatafr.txt", header=T, sep="\t", quote="", dec=".")
  g &lt;- ggplot() + 
  geom_polygon(data = plotDatafr, aes(x=long, y = lat, group = group, fill=item), alpha=0.8, colour = "black") + 
  scale_fill_manual(values = c("#009E73", "#F0E442", "#0072B2", "#D55E00"), na.value=NA) + 
  theme_nothing(legend = TRUE) +
  coord_map() #avoid distorsion
  ggsave(g, filename = "crayon_euro.png", scale=1) #save for futher use
  </code></pre>
  
  <p>I tried to use the "scale_fill_distiller" command, but with such command I can only plot the properties of a single item, and I loose their given colors, for example:</p>
  
  <pre><code>g &lt;- ggplot() + 
  geom_polygon(data = plotDatafr, aes(x = long, y = lat, group = group, fill = score), colour = "black", alpha = 0.8) +
  scale_fill_distiller(palette = "Purples", breaks = pretty_breaks(n = 9), labels = percent, direction = 1, "", guide=FALSE) +
  guides(fill = guide_legend(reverse = TRUE, override.aes = list(alpha = 1))) +
  theme_nothing(legend = TRUE) + 
  coord_map() #avoid distorsion
  ggsave(g, filename = "crayon_euro.png", scale=1) #save for futher use
  </code></pre>
  
  <p>Does anyone have any idea how I can make the different my polygons shades varying according to their numerical value? I can't figure a way to combine scale_fill_distiller and scale_fill_manual in the same time.</p>