Directional statistics is the subdiscipline of statistics that deals with directions (unit vectors in Rn), Cartesian Coordinate System|axes (lines through the origin in Rn) or rotations in Rn. More generally, directional statistics deals with observations on compact Riemannian manifolds.
The fact that 0 degree (angle)|degrees and 360 degrees are identical angles, so that for example 180 degrees is not a sensible average|mean of 2 degrees and 358 degrees, provides one illustration that special statistical methods are required for the analysis of some types of data (in this case, angular data). Other examples of data that may be regarded as directional include statistics involving temporal periods (e.g. time of day, week, month, year, etc.), compass directions, dihedral angles in molecules, orientations, rotations and so on.