A Discrete Global Grid System is aligned if all parent cell points are also child cell points (See Centroid Child, Centroid Parent, Vertex Child, Vertex Parent). If a DGGS does not have this property, it is defined as unaligned. Cartesian Coordinates is an example of an aligned adressing system. A Quad-tree is and example of an unaligned data struture. An aligned data structure can not be congruent.