Remove border lines in ggplot map/choropleth

Question

I would like to remove the lines between regions of a choropleth generated in ggplot. My question is motivated by a very large map with very very small regions

Answer 1

Setting color = NA works for me:

ggplot(tn, aes(x = long, y = lat, group = group)) + 
    geom_polygon(aes(fill = group), color = NA) +
    coord_map()

produces this plot with no spaces between polygons.

I'm using ggplot2 version 1.0.0.

I added coord_map to give it the right aspect ratio. On my machine, that doesn't affect the borders, I'm not sure why borders are visible in your second post. Here's mine:

ggplot(tn, aes(x = long, y = lat, group = group)) + 
  geom_polygon(aes(fill = group), color = NA)