Simulating Trade Routes

[isomage]

For my random Traveller subsector maps I connected each A, B, or C type starport with up to two random nearest neighbors of the same or better type; lower types are left unconnected. This typically results in treelike connectivity (though loops occasionally form) with A ports being hubs for B ports, which are in turn hubs for C ports. It's a pretty simple algorithm and seems to give reasonable-looking results.

It's not as involved as what you're trying to do, but maybe you'd find the basic idea applicable at some level -- connecting cities to random nearest neighbors of the same or greater population would give the same kind of routes.