Change Point Size in Graphs in R

A scatterplot is one of the most basic and popularly-used plots in R. It simply plots a point depending on the value of two variables, each at the x and the y-axis, respectively. Scatterplots can help identify any underlying pattern between these variables and show how the values are related to each other.

The following example shows a simple scatterplot graph using the plot() function:

v1 <- c(1,2,3,4,11,9,7)
v2 <- c(3,4,5,6,3,2,1)
plot(x = v1, y = v2, xlab = "X Axis",ylab = "Y Axis",
     main = "Sample Scatterplot")

Basic Scatter plot in R

Notice that we use the xlab, ylab, and main parameter to add the title and labels of X and Y axes.

We can set the size and the shape of the points using the pch and the cex parameters.

In R, we can have different symbols for a plot. We can have a simple empty circle, square, triangle, or filled shapes, and many more. We use the pch parameter to specify the shape of the point.

The pch value ranges from 1 to 25, corresponding to different shapes.

In the code below, we will set the pch to 20.

plot(x = v1, y = v2, xlab = "X Axis",ylab = "Y Axis",
     main = "Sample Scatterplot", pch = 20)

Scatter plot with pch parameter in R

We can use the cex argument to set the size of the points to make them more readable. This parameter is generally used with the par function to set other plotting parameters, but here we use it in the plot function as shown below.

plot(x = v1, y = v2, xlab = "X Axis",ylab = "Y Axis",
     main = "Sample Scatterplot", pch = 20, cex = 2)

Scatter plot with cex parameter in R

Notice the difference in the graph above and how the size of the points has increased.

In case you use the qplot() function to plot the scatter plot, we can set the size of the points using the size parameter. See the following code.

qplot(v1,v2, size= I(5))

Scatter plot with qplot function in R

The same parameter can also be applied while using the ggplot() function.