Answer
Horizontal plane
Work Step by Step
Conversion of rectangular to spherical coordinates is as follows:
$x=\rho \sin \phi \cos \theta; y=\rho \sin \phi \sin \theta;z=\rho \cos \phi$
and
$\rho=\sqrt {x^2+y^2+z^2}$;
$\cos \phi =\dfrac{z}{\rho}$; $\cos \theta=\dfrac{x}{\rho \sin \phi}$
Here, $\rho \cos \phi=1$
This implies that
$z=1$
This shows that $z=1$ is a horizontal plane parallel to the xy plane with z-intercept at $1$.
