International
Tables for Crystallography Volume A Spacegroup symmetry Edited by M. I. Aroyo © International Union of Crystallography 2016 
International Tables for Crystallography (2016). Vol. A, ch. 3.1, p. 710
Figure 3.1.3.1
P. M. de Wolff^{c}


Figure 3.1.3.1
The net of lattice points in the plane of the reduced basis vectors a and b; OBAD is a primitive mesh. The actual choice of a and b depends on the position of the point P, which is the projection of the point in the next layer (supposed to lie above the paper, thin dashed lines) closest to O. Hence, P is confined to the Voronoi domain (dashed hexagon) around O. For a given interlayer distance, P defines the complete lattice. In that sense, P and represent identical lattices; so do Q, and , and also R and . When P lies in a region marked (hatched), the reduced typeII basis is formed by , and . Regions marked (crosshatched) have the reduced typeI basis and . Small circles in O, M etc. indicate twofold rotation points lying on the region borders (see text). 