title: Edit boundaries in a map with ggplot2
body: <p>I have created a map with <code>ggplot2</code>. So far I am happy with my plot but I was wondering whether it is possible to edit the boundaries that separate each of the regions within the map. I know that adding <code>geom_path()</code> you can explicitly incorporate them but I have not figured out how to edit the level of thickness. Is anyone familiar with how to do this? Many thanks in advance. </p>
  
  <p>The code I have used is the following: </p>
  
  <pre><code>library(ggplot2)
  library(RColorBrewer)
  
  ex_sector = ggplot(data_mapping, aes(long, lat, group=group, fill = entry_cat)) +
    scale_fill_brewer(type = "seq", palette = "Greens") + geom_polygon()  + geom_path(colour = "black")
   ggsave("test_fill.png", ex_sector, scale = 0.5)
  </code></pre>
  
  <p>An the output is:</p>
  
  <p><a href="https://i.stack.imgur.com/gqLPs.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/gqLPs.png" alt="enter image description here"></a></p>