  Graphs are called navigable if one can find short paths through them using
only local knowledge. It has been shown that for a graph to be navigable, its
construction needs to meet strict criteria. Since such graphs nevertheless seem
to appear in nature, it is of interest to understand why these criteria should
be fulfilled.
  In this paper we present a simple method for constructing graphs based on a
model where nodes vertices are ``similar'' in two different ways, and tend to
connect to those most similar to them - or cluster - with respect to both. We
prove that this leads to navigable networks for several cases, and hypothesize
that it also holds in great generality. Enough generality, perhaps, to explain
the occurrence of navigable networks in nature.
