Most of the filtering is on categorical variables, but notice that the continuous variable of age is collapsed into a categorical variable dividing people into three groups: 15-24 years old, 24-44 years old, and 45 years or older.
To produce informative graphics that tell a clear story, data journalists often need to turn a continuous variable into a categorical variable by dividing it into bins. But how do you select the range of values for each bin?