Scatter charts use two variables to plot points and makes it clear where there are congregations. The data points make up the X and Y coordinates. The labels on the X axis are separate from the X units, allowing you to "group" them. For example, like the example, you could set the maxium X value to be 365, but only have four labels. That way you would have a granularity of a day, but the X axis would only have four labels. Like the example.