title: Fill Geospatial polygons with pattern - R
body: <p>I have a map of Bosnia with municipalities colored according to the ethnic majority living there.
  However, I would like to use different patterns instead of colors (or grey scales), as it's going to be printed in black and white.<br>
  I have searched, but couldn't find a way to do it. Does anyone have an idea on how to do this?
  <a href="https://www.dropbox.com/s/bfa1dwozq5rbsuo/Bosnia.zip" rel="noreferrer">Link to shapefile</a></p>
  
  <p>Here's my code so far:</p>
  
  <pre><code>library(RColorBrewer)
  library(maptools)
  library(rgdal)
  library(rgeos)
  library(ggplot2)
  library(gridExtra)
  
  setwd("path")
  
  bosnia &lt;- readOGR("path/to/file", "bosnia_analysis", 
                  verbose = TRUE, stringsAsFactors = FALSE)
  
  bosnia &lt;- readShapePoly("path/to/bosnia_analysis.shp",proj4string=CRS("+proj=longlat +datum=WGS84"))
  bosnia.df &lt;- bosnia@data
  
  serbs &lt;- bosnia[bosnia$SEPRIORITY &gt; bosnia$CRPRIORITY &amp; bosnia$SEPRIORITY &gt; bosnia$MOPRIORITY,]
  croats &lt;-  bosnia[bosnia$CRPRIORITY &gt; bosnia$SEPRIORITY &amp; bosnia$CRPRIORITY &gt; bosnia$MOPRIORITY,]
  moslems &lt;- bosnia[bosnia$MOPRIORITY &gt; bosnia$CRPRIORITY &amp; bosnia$MOPRIORITY &gt; bosnia$SEPRIORITY,]
  
  p &lt;- ggplot(bosnia, aes(x = long, y = lat, group = group)) + 
    geom_polygon(aes(x=long,y=lat,group=group), fill="white", colour="grey") +
    geom_polygon(data=serbs, aes(x=long,y=lat,group=group), fill="black", colour="grey") +
    geom_polygon(data=croats, aes(x=long,y=lat,group=group), fill="green", colour="grey") +
    geom_polygon(data=moslems, aes(x=long,y=lat,group=group), fill="red", colour="grey") +
    # Styling
    coord_map() +
    labs(x="Bosnia", y=" ") + 
    theme_bw() + 
    theme(panel.grid.minor=element_blank(), panel.grid.major=element_blank()) + 
    theme(axis.ticks = element_blank(), axis.text.x = element_blank(), axis.text.y = element_blank()) + 
    theme(panel.border = element_blank())
  
  p
  </code></pre>
  
  <p>This gives me the following map:
  <img src="https://i.stack.imgur.com/uiIOV.png" alt="enter image description here"></p>