I am making a choropleth using ggplot2 with the county dataset. The data I am tying in to the county data is only for a handful of counties. My questions is: how can I change the default grey fill for the counties in which I don't have data? In the merged dataset there are just na's for the mapped values in the grey counties.
Code:
ggplot(data, aes(long, lat, group=group)) +
geom_polygon(aes(fill=`Surface Mines`), col="grey") +
coord_map("polyconic") +
scale_fill_continuous(low="yellow", high="red") +
geom_path(data=state , colour="black") +
theme_void()