If you are already familiar with the graphics package, you know that in R, you have the opportunity to create plot windows on which you can arrange multiple plots. In ggplot2, there is no single function available to do that, but you will need to become familiar with certain basic concepts of the grid package, which was used to build ggplot2. In grid, you have the possibility of defining viewports, which are rectangular regions on a graphics device, and plots can be assigned to these regions. In order to do that, we can use a grid function called viewport(). Using this method, you have two main ways of combining multiple plots:
Arranging plots by specifying the plot position in terms of rows and columns
Specifying the exact position of each plot
In the following sections, we will see examples of both methods.