Setting the Aspect Ratio of R Plots

How to adjust the aspect ratio of R plots with the asp parameter.

Note

Original Japanese version: Rのプロットのアスペクト比を設定する方法

In R plotting functions such as plot(), the aspect ratio can be set with the asp parameter. The aspect ratio specifies how many times the unit length of the y-axis is relative to the unit length of the x-axis.

Example of the asp Parameter

You can adjust the aspect ratio by specifying the asp parameter inside plot().

plot(1:10, 1:10) # default aspect ratio

plot(1:10, 1:10, asp = 1) # aspect ratio 1:1

In the example above, asp = 1 is set, so the unit lengths of the x-axis and y-axis are equal. If asp = 2 is set, the unit length of the y-axis becomes twice that of the x-axis.

plot(1:10, 1:10, asp = 2)

Adjusting the Aspect Ratio Including the Plot Region

This is useful when making a 1:1 plot, such as when drawing a 1:1 line. Depending on the shape of the plot region, the actual display may not become square. In that case, you can also use par(pty = "s") to set the plot region to a square.

par(pty = "s") # set the plot region to a square

x <- rnorm(10, mean = 1, sd = 0.1) * 1:10
y <- rnorm(10, mean = 1, sd = 0.1) * 1:10

plot(x, y, asp = 1)
plot(x, y, asp = 1)
abline(0, 1, lty = 2)

par(pty = "m") # restore the plot region setting

NoteSupplement

• rnorm(): generates random numbers following a normal distribution. Here it generates random numbers with mean 1 and standard deviation 0.1.
• abline(0, 1, lty = 2): draws the line y = x as a dashed line. lty = 2 means a dashed line.