e>b</code> are used in
the naming convention to distinguish between the two objects
(e.g. dist.net1.a and dist.net1.b). The matrices that these
objects represent are not necessarily square. In matrices of type
<code>a</code>, rows correspond to observed locations and columns to
prediction locations. In contrast, rows correspond to prediction
locations and columns to observed locations in matrices of type
<code>b</code>. Direction is also preserved, with columns representing
the FROM site and rows representi