Is there a way in which I can overlay state boundaries with county maps in the usmap R package?

Question

I am trying to have the state boundaries clearly demarcated along with the county wise heat maps. But the state boundaries do not seem prominent. I have tried a couple of different code chunks but both do not work.

# Code chunk1
# Obtain state polygon data for all states
states_sf <- get_urbn_map(map = "states", sf = TRUE)

# Filter state polygon data for specified states
selected_states <- c("AL", "AR", "CT", "DC", "DE", "FL", "GA", "LA", 
                     "MA", "MD", "ME", "MS", "NC", "NH", "NJ", "NY", 
                     "PA", "RI", "SC", "TX", "VA", "VT", "WV")
selected_states_sf <- states_sf[states_sf$ST %in% selected_states, ]

# Assuming Hurricane$total_wind is a numeric variable in Hurricane dataset
plot_usmap("counties", data = Hurricane, values = "total_wind",
           include = selected_states,
           color = "black"
) +
  ggplot2::scale_fill_continuous(low = "snow2", high = "red", guide = FALSE) +
  geom_sf(data = selected_states_sf, fill = NA, color = "black", size = 0.5) +  # Adjusted size for state borders
  theme_minimal() +
  
  # Remove grid lines from plot
  coord_sf(datum = NA, crs = st_crs(states_sf)) +   # Explicitly set the coordinate system
  labs(fill = "Random Data") + 
  scale_fill_gradient2(low='snow2', high='red') + 
  theme_bw() + 
  theme(
    # Hide panel borders and remove grid lines
    panel.border = element_blank()
  )

#Code chunk2
plot_usmap("counties", data = Hurricane, values = "total_wind",
           include = c("AL", "AR", "CT", "DC", "DE", "FL", "GA", "LA", 
                       "MA", "MD", "ME", "MS", "NC", "NH", "NJ", "NY", 
                       "PA", "RI", "SC", "TX", "VA", "VT", "WV")
) +
  ggplot2::scale_fill_continuous(low = "ghostwhite", high = "red", guide = FALSE)

Answer 1

Update The usmap has been modernized in version 0.7.0 and now returns map data as simple features, i.e. geom_polygon will no longer work. Instead we have to use geom_sf:

library(usmap)
library(ggplot2)

selected_states <- c(
  "AL", "AR", "CT", "DC", "DE", "FL", "GA", "LA",
  "MA", "MD", "ME", "MS", "NC", "NH", "NJ", "NY",
  "PA", "RI", "SC", "TX", "VA", "VT", "WV"
)

selected_states_df <- usmap::us_map(include = selected_states)

plot_usmap("counties",
  # data = Hurricane, values = "total_wind",
  include = selected_states,
  color = "black"
) +
  geom_sf(
    data = selected_states_df,  
    color = "blue", fill = NA, linewidth = 1
  ) +
  scale_fill_gradient2(low = "snow2", high = "red") +
  theme(
    panel.border = element_blank()
  ) +
  labs(fill = "Random Data")

Original answer

One option would be to add the state boundaries using a geom_polygon and the state map data provided by the usmap package which you can get using usmap::us_map.

library(usmap)
library(ggplot2)

selected_states <- c(
  "AL", "AR", "CT", "DC", "DE", "FL", "GA", "LA",
  "MA", "MD", "ME", "MS", "NC", "NH", "NJ", "NY",
  "PA", "RI", "SC", "TX", "VA", "VT", "WV"
)

selected_states_df <- usmap::us_map(include = selected_states)

plot_usmap("counties",
  # data = Hurricane, values = "total_wind",
  include = selected_states,
  color = "black"
) +
  geom_polygon(
    data = selected_states_df,
    aes(x = x, y = y, group = group),
    color = "blue", fill = NA, linewidth = 1
  ) +
  scale_fill_gradient2(low = "snow2", high = "red") +
  theme(
    panel.border = element_blank()
  ) +
  labs(fill = "Random Data")