The figure builds up further when we put the representation for two samples over the top, The 2 shell .  To achieve this, I have given the wave with 2 samples an amplitude of 2.  This is simply to visualise all the sample points on the same diagram.  So this diagram shows the 1 shell and the 2 shell.  Note how the initial condition and second sample lies on the exclusion line from the 1 shell.