Scatter plots are plots of symbols at the data points in a field. The symbols may be sized according to the values of a specified variable, colored by the values of the contour variable, or may be uniformly sized or colored. Unlike contour plots, scatter plots do not require any mesh structure connecting the points, this allows you to make scatter plots of irregular data.
To add a scatter layer to your plot, activate the "Scatter" toggle in the Plot sidebar. You can modify your Scatter plot using the Scatter page of the Zone Style dialog and the Scatter submenu of the Plot menu.