area-plot.utf8

An area plot is very similar in appearance to a line plot. It represents a data series based on two numerical variables in the form of a simple line “joining the dots”; however, the area under the line is filled. When more than one response variable is represented, the area plot becomes a multiple or stacked area plot which helps visualize how different components contribute to a total/sum (this will be further explained here).

Let’s see here how to use ggplot() to draw such a plot. We will consider the following example where precipitations were measured daily at Lygra, Hordaland in January 2020. Here is the dataframe:

# dataframe
df <- data.frame(day, precipitations)
str(df)

## 'data.frame':    31 obs. of  2 variables:
##  $ day           : int  1 2 3 4 5 6 7 8 9 10 ...
##  $ precipitations: num  0.4 9.8 9 3.2 21.6 14.4 20.2 3 3.6 0.2 ...

We map the variables with aes(day, precipitations) and use geom_area() to draw the plot:

ggplot(df, aes(day, precipitations)) +
  geom_area()

As usual, you may change the look of the plot with a handful of arguments. With fill= and alpha=, you may change the color of the area and its transparency, respectively:

ggplot(df, aes(day, precipitations)) +
  geom_area(fill="darkblue", alpha=.5)

If you are interested in plotting only one fragment of the data series, you can use ifelse() in aes(). You may for instance decide to display only the first 15 days of the month with time<=12:

ggplot(df, aes(day, precipitations)) +                       
  geom_area(aes(x = ifelse(day<=15, day, NA))) +
  xlim(1,31)

## Warning: Removed 16 rows containing missing values (position_stack).

Note the warning message telling you that some data has been excluded (as expected).

Alternatively you can highlight a specific interval of the area plot (for example the period January 10^th-23^th) by making a two-layered area plot: a first geom_area() layer shows the whole interval from January 1^st to 31^st in dark and a second layer geom_area() shows only the interval January 10^th-23^th in orange on top of (and thus hiding) the first layer:

ggplot(df, aes(day, precipitations)) +
  geom_area(fill="darkslategrey") +
  geom_area(aes(x = ifelse(day>=10 & day<=23, day, NA)), fill="orange")

## Warning: Removed 17 rows containing missing values (position_stack).

Adding plot title, axis titles, ticks, labels and other essential elements

In this section, you will learn how to set/modify all the necessary elements that make a plot complete and comprehensible. Such elements are: