Visual representation of the domain and range of a function? An excerpt in the book "College Algebra by Michael Sullivan is that:

When the graph of a function is given, its domain may be viewed as the shadow created by the graph on the x- axis by vertical beams of light. Its range can be viewed as the shadow created by the graph on the y-axis by horizontal beams of light.

I did't get it and i also sought in google to get some idea but i can't find one.
Can anyone help me to understand it maybe with some graphics.
Thanks.
 A: The naive definition of domain and range are represented in the following figure



*

*the domain is the set of all $x$ values such that $y=f(x)$ is defined (and unique)

*the range is the set of all $y$ values such that  $\exists x$ (at least one) and $y=f(x)$
A: Consider a particular point on the function. If you cast a vertical light beam through that point it would cast a shadow on the x-axis according to the x value of that point. Since the domain is the set of all possible x values of a function, imagine repeating the vertical light beams on every point on the function. Then the resulting shadow on the x-axis represents the domain. It is a set of values on the x-axis. By a similar process you can represent the range on the y-axis.
A: This is not meant to be difficult. It says that going perpendicularly down/up from each $(x,f(x))$ (parallel to $y $-axis) we reach the $x$ point (point of which $f(x) $ is the image).
So 'projecting' all $(x,f(x))$  onto the $x $-axis gives the domain.
And similarly for the 'shadow' on the $y$-axis.
