which unit vector points in the positive direction of the z axis
Unit vector The unit vectors appropriate to spherical symmetry are:    r ^   {\displaystyle \mathbf {\hat {r}} } , the direction in which the radial distance from the origin increases;    φ ^   {\displaystyle {\boldsymbol {\hat {\varphi }}}} , the direction in which the angle in the x-y plane counterclockwise from the positive x-axis is increasing; and    θ ^   {\displaystyle {\boldsymbol {\hat {\theta }}}} , the direction in which the angle from the positive z axis is increasing. To minimize redundancy of representations, the polar angle   θ  {\displaystyle \theta }  is usually taken to lie between zero and 180 degrees. It is especially important to note the context of any ordered triplet written in spherical coordinates, as the roles of    φ ^   {\displaystyle {\boldsymbol {\hat {\varphi }}}}  and    θ ^   {\displaystyle {\boldsymbol {\hat {\theta }}}}  are often reversed. Here, the American "physics" convention[1] is used. This leaves the azimuthal angle   φ  {\displaystyle \varphi }  defined the same as in cylindrical coordinates. The Cartesian relations are:
Abscissa and ordinate Usually these are the horizontal and vertical coordinates of a point in a two-dimensional rectangular Cartesian coordinate system. The terms can also refer to the horizontal and vertical axes respectively (typically x-axis and y–axis) of a two-dimensional graph. An ordered pair consists of two terms—the abscissa (horizontal, usually x) and the ordinate (vertical, usually y)—which define the location of a point in two-dimensional rectangular space.