  We analyse the results of our experimental laboratory approximation of
motorways networks with slime mould Physarum polycephalum. Motorway networks of
fourteen geographical areas are considered: Australia, Africa, Belgium, Brazil,
Canada, China, Germany, Iberia, Italy, Malaysia, Mexico, The Netherlands, UK,
USA. For each geographical entity we represented major urban areas by oat
flakes and inoculated the slime mould in a capital. After slime mould spanned
all urban areas with a network of its protoplasmic tubes we extracted a
generalised Physarum graph from the network and compared the graphs with an
abstract motorway graph using most common measures. The measures employed are
the number of independent cycles, cohesion, shortest paths lengths, diameter,
the Harary index and the Randic index. We obtained a series of intriguing
results, and found that the slime mould approximates best of all the motorway
graphs of Belgium, Canada and China, and that for all entities studied the best
match between Physarum and motorway graphs is detected by the Randic index
(molecular branching index).
