ggplot2 mapping county boundries in one color and state boundries in another on the same map

Question

I am creating a choropleth county map with grey borders, and I also want to include the state boundries in black. Does anyone know how I go about adding a second layer of state

Answer 1

Just add a geom_path to your code...

I used red to highlight the boundaries but you can easily just set it to black.

    ggplot( wip_map, aes( x = long , y = lat , group=group ) ) +
        geom_polygon( colour = "grey" , aes( fill = factor( CATEGORY ) ) ) +
        scale_fill_manual( values = pal ) +
        expand_limits( x = wip_map$long, y = wip_map$lat ) +
        coord_map( "polyconic" ) + 
        labs(fill="Number Per\nCounty") + 
        theme_clean( ) +
        geom_path( data = state_map , colour = "red")