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ggplot2 geom_polygon() in R: Filled Closed Shapes

The geom_polygon() function in ggplot2 draws filled CLOSED shapes from a sequence of x and y coordinates. It is essential for map plots, custom shapes, and area fills.

By Selva Prabhakaran  ·  Published May 12, 2026  ·  Last updated May 12, 2026
⚡ Quick Answer
ggplot(df, aes(x, y)) + geom_polygon()
ggplot(df, aes(x, y, group = id, fill = id)) + geom_polygon()
ggplot(map_data("world"), aes(long, lat, group = group)) + geom_polygon()
geom_path(...)                          # different: open path

Need explanation? Read on for examples and pitfalls.

📊 Is geom_polygon() the right tool?
STARTclosed filled shapegeom_polygon()map regionsgeom_polygon (or geom_sf for sf objects)open pathgeom_path()rectanglegeom_rect()multiple polygonsaes(group = id)

What geom_polygon() does in one sentence

geom_polygon() connects points in row order, closes the loop (last to first), and fills the interior. Used for maps, custom shapes, and area fills.

Syntax

geom_polygon(mapping = NULL, data = NULL, fill = "grey50", ...). Always uses row order to determine vertices.

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RWorld map
library(ggplot2) library(maps) ggplot(map_data("world"), aes(long, lat, group = group)) + geom_polygon(fill = "lightgrey", color = "black")

  

  





Tip
For maps, ALWAYS pass group = group in aes. Otherwise polygons connect across regions, producing visual artifacts.



Five common patterns



1. Simple polygon




  

    
RTriangle

    
df <- tibble(x = c(0, 1, 0.5), y = c(0, 0, 1))
ggplot(df, aes(x, y)) + geom_polygon()

    

      
      
    

    

  

  





2. Multiple polygons via group




  

    
RTwo triangles

    
df <- tibble(
  x = c(0,1,0.5,  2,3,2.5),
  y = c(0,0,1,    0,0,1),
  id = c("A","A","A","B","B","B")
)
ggplot(df, aes(x, y, group = id, fill = id)) +
  geom_polygon()

    

      
      
    

    

  

  





3. World map




  

    
RCountry boundaries

    
ggplot(map_data("world"), aes(long, lat, group = group)) +
  geom_polygon(fill = "white", color = "grey50")

    

      
      
    

    

  

  





4. Choropleth via fill




  

    
RColor regions by metric

    
us_states <- map_data("state")
metrics <- tibble(region = unique(us_states$region), value = runif(49))

us_states |>
  left_join(metrics, by = "region") |>
  ggplot(aes(long, lat, group = group, fill = value)) +
  geom_polygon(color = "white") +
  coord_map()

    

      
      
    

    

  

  





5. Custom shape with alpha




  

    
RTranslucent polygon over points

    
ggplot(mtcars, aes(wt, mpg)) +
  geom_point() +
  geom_polygon(data = tibble(wt = c(2,4,4,2), mpg = c(20,20,30,30)),
               fill = "yellow", alpha = 0.3)

    

      
      
    

    

  

  





Key Insight
Polygons need group to keep boundaries separate. Without group, ggplot connects all points into one giant polygon. Always provide group when plotting multiple regions.



geom_polygon() vs geom_rect() vs geom_sf()







Function
Inputs
Best for






geom_polygon()
x, y per vertex
Custom polygons / maps




geom_rect()
xmin, xmax, ymin, ymax
Rectangles




geom_sf()
sf objects
Modern map data







For modern map work, geom_sf with the sf package is often easier than geom_polygon.



A practical workflow



Map plotting is geom_polygon's signature use case.




  

    
RInteractive R

    
us_data <- map_data("state") |>
  left_join(state_metrics, by = "region")

ggplot(us_data, aes(long, lat, group = group, fill = value)) +
  geom_polygon(color = "white", linewidth = 0.2) +
  coord_map() +
  scale_fill_viridis_c() +
  theme_void()

    

      
      
    

    

  

  





Standard choropleth recipe.



Common pitfalls



Pitfall 1: forgetting group. Without it, polygons join into one tangled mess. Always set group for maps.



Pitfall 2: confusing with geom_path. geom_path is OPEN; geom_polygon is CLOSED and FILLED.



Warning
geom_polygon() requires vertices in ORDER (clockwise or counterclockwise). Random row order produces self-intersecting polygons.



Try it yourself





Try it: Plot a simple square polygon. Save to ex_plot.



  

    
RYour turn: a square

    
df <- tibble(x = c(0, 2, 2, 0), y = c(0, 0, 2, 2))

ex_plot <- df |>
  # your code here

    

      
      
    

    

  

  





Click to reveal solution



  

    
RSolution

    
ex_plot <- ggplot(df, aes(x, y)) +
  geom_polygon(fill = "steelblue") +
  coord_fixed()

    

      
      
    

    

  

  





Explanation: Four vertices in order; geom_polygon closes the loop and fills.










After mastering geom_polygon, look at:



    


  • geom_path(): open path
    • 


  • geom_rect(): rectangles
    • 


  • geom_sf(): sf objects (maps)
    • 


  • coord_map() / coord_sf(): map projections
    • 


  • geom_ribbon(): between-curves area
    • 





FAQ



What does geom_polygon do in ggplot2?



geom_polygon() draws filled closed shapes from x and y coordinates connected in row order.



Why do I need group in geom_polygon?



To distinguish multiple polygons. Without it, all points connect into one polygon. Group separates them.



What is the difference between geom_polygon and geom_path?



geom_polygon CLOSES the loop and FILLS. geom_path is open (no fill, no auto-close).



Should I use geom_polygon or geom_sf for maps?



For modern sf-based map data, geom_sf is easier. For traditional data frames from maps package, geom_polygon is the standard.



Can I have holes in a polygon?



geom_polygon does not natively support holes. Use geom_sf with sf objects for proper polygon-with-holes support.



          

        


        
      


      

        

        
© 2016-2026 Selva Prabhakaran.
          This work is licensed under the Creative Commons License.
        

        

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