The display order of dimension groups is determined by the ranking of the individual dimensions within the groups.
A dimension group inherits the highest rank of its member dimensions. For example, if the highest-ranked dimension in dimension Group A is ranked higher than the highest-ranked dimension in Group B, then group A will be ordered before group B.
Dimension groups are also ranked relative to dimensions that are not included in groups. Continuing the previous example, if Dimension XYZ has a rank that is lower than Group A but higher than Group B, the ranking would look like this:
Group A
Dimension XYZ
Group B
Dimensions with the same rank are ordered alphanumerically by name. It is important to note that dimension name, not dimension group name, determines the display order of dimension groups in this situation. Dimension groups are ordered according to their highest alphanumerically ranked member dimension. So dimension group Z, which contains dimension H, will be ordered before dimension group A, which contains dimension I.
For more information on ranking, see Ranking dimensions manually.