Transportation hubs key to the flow of the Gospel

In his study of the early church, Rodney Stark noted that there was a strong correlation between cities that had transportation hubs and cities that received the Gospel early on. This makes sense, because the Gospel flows by people through daily life.

It seems obvious that cities that are transportation hubs today would also be strategic for early church planting. They are easier to reach, and from them the Gospel can flow to nearby connected cities in the course of “normal daily life.” These have sometimes been called “Gateway Cities.”

So, it follows that developing a “transportation hub index” of some kind, rating the world’s provinces & districts by this index, and then prioritizing unreached transportation hubs would be a key piece of research, right?

Here’s an initial stab at such an index:

0 = No roads 1 = Very few roads of any kind 2 = Dirt roads or other traffic methods 3 = Paved roads 4 = Provincial center with good roads 5 = Large city (e.g. 100,000+) connected by a major highway 6 = Megacity connected by a major highway 7 = Presence of a domestic airport or other logistical hub (e.g. railway, seaport) 8 = Presence of an international airport with regional international connections 9 = Presence of a major international airport (such as is found at London)

What adjustments might you recommend?