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Plotting Illinois with ggmap and ggplot in r

I am trying to plot out a base map of Illinois by counties. Libraries I had loaded:

library(ggplot2)
library(maps)
library(ggmap)
library(mapdata)

This is my code:

states <- map_data("state")
IL <- subset(states, region %in% c("illinois"))
counties <- map_data("county")
IL_county <- subset(counties, region == "illinois")

il_base <- ggplot(data = IL, mapping = aes(x = long, y = lat)) + 
  coord_fixed(1.3) + 
  geom_polygon(color = "black", fill = NA) + 
  theme_nothing()
il_base 

il_base + 
  geom_polygon(data = IL_county, fill = NA, color = "black") +
  geom_polygon(color = "black", fill = NA)

The il_base plot is fine, it shows a basic outline of the state. However, as soon as I add geom_polygon to this it maps the counties out like this:

IL

And this is NOT what the counties of IL look like. What did I do wrong here?

Solution

  • I solved the problem by modifying the base plot to:

    # Add group
il_base <- ggplot(data = IL, mapping = aes(x = long, y = lat, group = group)) + 
  coord_fixed(1.3) + 
  geom_polygon(color = "black", fill = NA) + 
  theme_nothing()