Merging CSV with Shapefile to produce Maps in R

In this video, I demonstrated how to generate maps after merging CSV with a shapefile in R.
To circumvent the many codes for plotting the nice ggmap, you can use the code below to produce a simpler version
m1 = ggplot(shp_df, aes(x = long, y = lat, group = group, fill = HDI)) +
geom_polygon(color = "black", size = 0.1)
plot(m1)