The other half of the design of network data has to do with what ties or relations are to be
measured for the selected nodes. There are two main issues to be discussed here. In many
network studies, all of the ties of a given type among all of the selected nodes are studied --
that is, a census is conducted. But, sometimes different approaches are used (because they
are less expensive, or because of a need to generalize) that sample ties. There is also a
second kind of sampling of ties that always occurs in network data. Any set of actors might be
connected by many different kinds of ties and relations (e.g. students in a classroom might like
or dislike each other, they might play together or not, they might share food or not, etc.). When
we collect network data, we are usually selecting, or sampling, from among a set of kinds of
relations that we might have measured.