Mala Mahadevan looks at using R to describe data sets with two explanatory variables:
From the plot we can see that type 3 trees have the smallest circumference while type 4 have the largest, with type 2 close to type 4. We can also see that type 1 trees have the thinnest dispersion of circumference while type 4 has the highest, closely followed by type 2. We can also see that there are no significant outliers in this data.
Understanding whether variables are categorical or continuous is vital to understanding what you can and should do with them.