To construct two-dimension distribution of minor planets user should specify elements/ parameters/ function that will be plotted as abscissas and ordinates. In three-dimension case one should add to them the element plotted on Z axis. ... Though you may choose elements plotted along different axes at will, often there is good reason to plot such elements as a, n, or n" along X axis (two-dimension distributions) and to plot them along Y axis in three-dimension case. ...