  Hedayat et al. first introduced balanced sampling plans for the exclusion of
contiguous units. Wright detailed the results of a preliminary investigation of
two-dimensional balanced sampling plans avoiding adjacent units (2-BSAs), and
pointed out explicitly three types of 2-BSAs, which have different adjacency
scheme, namely "Row and Column", "Sharing a Border" and "Island". This paper
will provide more details for the three types of 2-BSAs from the point of view
of design theory.
