I'm using R and am trying to create a choropleth map using GISTools. My code is like:

choropleth(us_state, us_state$smallbiz1998, shades)
plot(us_interstate, add = TRUE)

us_state is a map of US states and us_interstate is a map of the interstate highways.

I want the boundaries of US states to be in gray. How can I do this?

choropleth documentation indicates that you can specify Additional parameters to be passed on to the plot method for sp.. However, when I try choropleth(us_state, us_state$smallbiz1998, shades, col = "gray") it throws an error.

(If it were changing the interstate highways to be gray, it's easy, just change the second line to plot(us_interstate, add = TRUE, col = "gray")).

1 Answer 1


Change the first line to choropleth(mn_county, mn_county$smallbiz1998, shades, border = "gray")

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