In Epidemiology, the horizontal axis (x-axis) is for the Independent variable, and the vertical axis (y-axis) is for the dependent variable.

The dependent variable is usually a frequency measure such as the number of cases or rate of disease.

For this lecture, I am including plotting techniques under graphing. Plotting can be referred to as mapping, or considered a separate category for organizing and displaying data. Whichever way, plotting is used to visually display data.