Example TGGHor.0: Suppose $y$ is a function of $x$ given by the equation $y = f (x) = 2x+ 3$.
The table, graph, and mapping diagram of this function have been created using GeoGebra.

In this mapping diagram, the axes are horizontal and the arrows point vertically from source axis down to target axis.

You can change the function by entering the value for $f(x)$ in the box of either the mapping diagram or the graph.

This visualization is not preferred:

GeoGebra: Table, graph, and mapping diagram (Horizontal Axes).