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:
Lateral mark Each mark indicates the edge of the safe water channel in terms of port (left-hand) or starboard (right-hand). These directions are relative to the direction of buoyage; this is usually a nominally upstream direction. In a river, the direction of buoyage is towards the river's source; in a harbour, the direction of buoyage is into the harbour from the sea. Where there may be doubt, it will be labelled on the appropriate chart. Often the cardinal mark system is used instead, when confusion about the direction would be common.