  Compared to the heavily studied surface drainage systems, the mountain ridge
systems have been a subject of less attention even on the empirical level,
despite the fact that their structure is richer. To reduce this deficiency, we
analyze different mountain ranges by means of a network approach and grasp some
essential features of the ridge branching structure. We also employ a fractal
analysis as it is especially suitable for describing properties of rough
objects and surfaces. As our approach differs from typical analyses that are
carried out in geophysics, we believe that it can initialize a research
direction that will allow to shed more light on the processes that are
responsible for landscape formation and will contribute to the network theory
by indicating a need for the construction of new models of the network growth
as no existing model can properly describe the ridge formation. We also believe
that certain features of our study can offer help in the cartographic
generalization. Specifically, we study structure of the ridge networks based on
the empirical elevation data collected by SRTM. We consider mountain ranges
from different geological periods and geographical locations. For each mountain
range, we construct a simple topographic network representation (the ridge
junctions are nodes) and a ridge representation (the ridges are nodes and the
junctions are edges) and calculate the parameters characterizing their
topology. We observe that the topographic networks inherit the fractal
structure of the mountain ranges but do not show any other complex features. In
contrast, the ridge networks, while lacking the proper fractality, reveal the
power-law degree distributions with the exponent $1.6\le \beta \le 1.7$. By
taking into account the fact that the analyzed mountains differ in many
properties, these values seem to be universal for the earthly mountainous
terrain.
