Consider some function $y=f(x)$. A standard graph has a horizontal axis for the independent variable ($x$) and a vertical axis for the dependent variable ($y$). Points are plotted to show $(x,f(x))$ pairs. In a mapping diagram the $x$ and $y$ axes are parallel. Ordered pairs are plotted as arrows from an $x$ value on the left number line to the corresponding $y$ value on the right axis.