The vertex and edge information in a SpatialGraph is
mapped into an igraph object
sg2igraph(sg, directed=FALSE)An igraph
SpatialGraph
whether the resulting igraph is directed
It is assumed that the SpatialGraph, used as input, is correct
(i.e.g all records in sg@e@data have the two first field correctly
identifying the field 'ID' in sg@v. It is also assumed that the
sg@e@data data.frame has the fields div and
len. These two are highly useful to conduct network operations
on the resulting igraph