tween two planning units following the
<em>Marxan</em> format. The <code>"boundary"</code> column should contain
binary <code>numeric</code> values that indicate if the two planning units
specified in the <code>"id1"</code> and <code>"id2"</code> columns are connected
or not. This data can be used to describe symmetric or
asymmetric relationships between planning units. By default,
input data is assumed to be symmetric unless asymmetric data is
also included (e.g., if data is present for planning units 2 an