  In many networks, the indegree of a vertex is a measure of its popularity.
Past research has studied indegree distributions treating the network as a
whole. In the US Patent citation network (USPCN), patents are classified into
categories and subcategories. A natural question arises: How do patents gather
their popularity from various (sub)categories? We analyse local indegree
distributions to answer this question.
  The citation (indegree) of a patent within the same category indicates its
internal popularity, while a cross-category citation indicates its external
popularity. We analyze the internal and external indegree distributions at each
level of USPCN hierarchy to learn how the internal and external popularity of
patents varies across (sub)categories.
  We find that all (sub)categories have local preferences that decide internal
and external patents' popularities. Different patents are popular in different
groups: Groups C1, C2 and C3 may not agree on popular patents in C1. In
general, patent popularity appears to be a highly local phenomenon with
subcategories (not even categories) deciding their own popular patents
independent of the other (sub)categories.
