  We propose a probabilistic growth model for transport networks which employs
a balance between popularity of nodes and the physical distance between nodes.
By comparing the degree of each node in the model network and the WAN, we
observe that the difference between the two is minimized for $\alpha\approx 2$.
Interestingly, this is the value obtained for the node-node correlation
function in the WAN. This suggests that our model explains quite well the
growth of airline networks.
