  In this paper, we show how certain three-class association schemes and
orthogonal arrays give rise to partial geometric designs. We also investigate
the connections between partial geometric designs and certain regular graphs
having three or four distinct eigenvalues, three-class association schemes,
orthogonal arrays of strength two and particular linear codes. We give various
characterizations of these graphs, association schemes and orthogonal arrays in
terms of partial geometric designs. We also give a list of infinite families of
directed strongly regular graphs arising from the partial geometric designs
obtained in this paper.
