  Robust and efficient design of networks on a realistic geographical space is
one of the important issues for the realization of dependable communication
systems. In this paper, based on a percolation theory and a geometric graph
property, we investigate such a design from the following viewpoints: 1)
network evolution according to a spatially heterogeneous population, 2)
trimodal low degrees for the tolerant connectivity against both failures and
attacks, and 3) decentralized routing within short paths. Furthermore, we point
out the weakened tolerance by geographical constraints on local cycles, and
propose a practical strategy by adding a small fraction of shortcut links
between randomly chosen nodes in order to improve the robustness to a similar
level to that of the optimal bimodal networks with a larger degree
$O(\sqrt{N})$ for the network size $N$. These properties will be useful for
constructing future ad-hoc networks in wide-area communications.
