2D density contour plots in ggplot2

The `geom_density_2d` function

A 2D density contour plot can be created in ggplot2 with geom_density_2d. You just need to pass your data frame and indicate the x and y variable inside aes.

# install.packages("ggplot2")
library(ggplot2)

# Data
set.seed(1)
df <- data.frame(x = rnorm(200), y = rnorm(200))

ggplot(df, aes(x = x, y = y)) +
  geom_density_2d()

Contour plot in R

Number of levels

It is possible to increase or decrease the number of levels with bins.

# install.packages("ggplot2")
library(ggplot2)

# Data
set.seed(1)
df <- data.frame(x = rnorm(200), y = rnorm(200))

ggplot(df, aes(x = x, y = y)) +
  geom_density_2d(bins = 15)

Type ?geom_contour for additional details.

Contour plot in ggplot2

Scatter plot with contour lines

Note that you can add the points with geom_point and then geom_density_2d to create a scatter plot with their corresponding contour lines.

# install.packages("ggplot2")
library(ggplot2)

# Data
set.seed(1)
df <- data.frame(x = rnorm(200), y = rnorm(200))

ggplot(df, aes(x = x, y = y)) +
  geom_point() + 
  geom_density_2d()

Scatter plot with contour in ggplot2

Color

You can customize the lines in several ways, changing the color, line type of size of the lines, as in other plots.

# install.packages("ggplot2")
library(ggplot2)

# Data
set.seed(1)
df <- data.frame(x = rnorm(200), y = rnorm(200))

ggplot(df, aes(x = x, y = y)) +
  geom_density_2d(color = "red")

2D density plot in ggplot2

Color based on the level

Passing ..level.. to the color argument of the aes will colorize each contour line based on the level. This will highlight the areas with higher density.

# install.packages("ggplot2")
library(ggplot2)

# Data
set.seed(1)
df <- data.frame(x = rnorm(200), y = rnorm(200))

ggplot(df, aes(x = x, y = y)) +
  geom_density_2d(aes(color = ..level..))

Contour plot in R with color based on the level

Change the color palette

If the lines are colored based on the level you can change the color palette with a continuous color palette. For instance, you can pass the scale_color_viridis_c to use the viridis palette.

# install.packages("ggplot2")
library(ggplot2)

# Data
set.seed(1)
df <- data.frame(x = rnorm(200), y = rnorm(200))

ggplot(df, aes(x = x, y = y)) +
  geom_density_2d(aes(color = ..level..)) +
  scale_color_viridis_c()

Contour plot color palette

Fill the contour with stat_density_2d

Note that there is a similar function named stat_density_2d that allows changing the geom used. If you set geom = "polygon" you can fill the contour as follows. Alternatively you can use geom_density_2d_filled.

# install.packages("ggplot2")
library(ggplot2)

# Data
set.seed(1)
df <- data.frame(x = rnorm(200), y = rnorm(200))

ggplot(df, aes(x = x, y = y, fill = ..level..)) +
  stat_density_2d(geom = "polygon")

Using the stat_density_2d function to fill a contour plot in R

The `geom_density_2d_filled` function

Basic filled contour in ggplot2

If you want to fill the areas of the contour based on the level you can use the geom_density_2d_filled function.

# install.packages("ggplot2")
library(ggplot2)

# Data
set.seed(1)
df <- data.frame(x = rnorm(200), y = rnorm(200))

ggplot(df, aes(x = x, y = y)) +
  geom_density_2d_filled()

Filled contour plot in ggplot2

Color palette

You can change the color palette with a fill scale, such as the scale_fill_brewer or scale_fill_manual for custom colors.

# install.packages("ggplot2")
library(ggplot2)

# Data
set.seed(1)
df <- data.frame(x = rnorm(200), y = rnorm(200))

ggplot(df, aes(x = x, y = y)) +
  geom_density_2d_filled() +
  scale_fill_brewer()

Filled contour color palette in R

Transparency

The alpha argument controls the transparency of the filled areas.

# install.packages("ggplot2")
library(ggplot2)

# Data
set.seed(1)
df <- data.frame(x = rnorm(200), y = rnorm(200))

ggplot(df, aes(x = x, y = y)) +
  geom_density_2d_filled(alpha = 0.75)

2D density filled contour in ggplot2 with lines

Filled contour with lines

Note that you can also add the contour lines over the filled contour.

# install.packages("ggplot2")
library(ggplot2)

# Data
set.seed(1)
df <- data.frame(x = rnorm(200), y = rnorm(200))

ggplot(df, aes(x = x, y = y)) +
  geom_density_2d_filled() +
  geom_density_2d(colour = "black")

Scatter plot with filled contour in ggplot2

Points and filled contour

It is worth to mention that you can add a filled contour over a scatter plot, setting a low transparency.

# install.packages("ggplot2")
library(ggplot2)

# Data
set.seed(1)
df <- data.frame(x = rnorm(200), y = rnorm(200))

ggplot(df, aes(x = x, y = y)) +
  geom_point() +
  geom_density_2d_filled(alpha = 0.4) +
  geom_density_2d(colour = "black")

Change the title of the legend of a contour plot in ggplot2

Title of the legend

The legend of the contour plots can be customized. In the following example we are changing the title of the legend.

# install.packages("ggplot2")
library(ggplot2)

# Data
set.seed(1)
df <- data.frame(x = rnorm(200), y = rnorm(200))

ggplot(df, aes(x = x, y = y)) +
  geom_density_2d_filled() +
  guides(fill = guide_legend(title = "Level"))