Finite element method approximation

[Mechanics_student]

In the picture above, we have on the left a figure representing spatial element, and on the right a figure representing reference element.

The type of element used in the method here is a linear quadrilateral element.

What I understand is moving or mapping from the reference element domain $$ where it seems that the quadrilateral element looks square; I don't understand why it is a square, to the spatial element domain $$, we use with such mapping the basis functions.

I think the basis functions $$ is what is giving us the quadrilateral shape?

For approximating spatial coordinates, $$ at $$ is approximated by the summation over the nodal values $$, (here $$ symbolizes node and $$ symbolizes direction), I'm not sure if $$ will be the average coordinate of the individual element since we're summing over the coordinates of each node.

Clarification is appreciated. Thank you.