There are many ways to construct a neighbourhood graph N for an arbitrary set of points G (a few are shown in Fig. ). In practice, G will be limited to a finite region of R N and we will not be primarily concerned with the boundary of points forming the convex hull H(G), but only the bulk B(G) = G\H(G). The goal when choosing a construction is to most closely preserve the topography of f (and topology thereof) when moving from its representation in R N to its representation on G. This leads to enforcing the following requirements for N :