Erik D. Demaine, Sándor P. Fekete, Günter Rote, Nils Schweer, Daria Schymura, Mariano Zelke. Integer point sets minimizing average pairwise L::1:: distance: What is the optimal shape of a town?. Comput. Geom., 44(2):82-94, 2011. [doi]
Abstract is missing.