type: int, default:
<shape default> (nodes) ,
1 (clusters) , minimum:
Set number of peripheries used in polygonal shapes and cluster boundaries.
Note that user-defined shapes are treated as a form of
box shape, so the default peripheries value is 1 and the user-defined shape
will be drawn in a bounding rectangle. Setting
peripheries=0 will turn this
peripheries=1 is the maximum value for clusters.