In order to provide a common interface to axes label angles some definitions need to be made. We have defined positive x to be from left to right and positive y and z (in a 3-D plot) to be from bottom to top. The angle is in reference to the positive axis and increases in a counter-clockwise direction. Above corresponds to positive angles, and below corresponds to negative angles.

For example, in a normal x-y plot with the x axis on the bottom and the y axis on the left, the labels are 
below the x axis and above the y axis. On a 3-D plot positive x and y go away from the corner at which the axes meet so that both x and y labels are below the axes. It might be helpful to think of the angles as being defined on an x axis and then rotated to the appropriate axis.