The Delaunay triangulation of a spatial point pattern X
  is defined as follows. First the Dirichlet/Voronoi tessellation of X
  computed; see dirichlet. Then two points of X
  are defined to be Delaunay neighbours if their Dirichlet/Voronoi tiles
  share a common boundary. Every pair of Delaunay neighbours is
  joined by a straight line.
The graph distance 
  in the Delaunay triangulation between two points X[i] and X[j]
  is the minimum number of edges of the Delaunay triangulation
  that must be traversed to go from X[i] to X[j].
This command returns a matrix D such that
  D[i,j] is the graph distance
  between X[i] and X[j].