X and Y Axes
An epidemic curve, or “epi curve,” is a visual display of the onset of illness among cases associated with an outbreak. The epi curve is represented by a graph with two axes that intersect at right angles.
The horizontal x-axis is the date or time of illness onset among cases.
The vertical y-axis is the number of cases.
Each axis is divided into equally spaced intervals, although the intervals for the two axes may differ.