You are right in everything you wrote, waldronate. I think the links I shared have more to do with cost of transport and how that interacts with the terrain constraints to create points where trade is more prevalent, hence where trading emporiums are likely to be based.

What I found most interesting is how those points change over time, with
1. the development of new trade routes, either as a result of exploration or technological innovation
2. the appearance of new resources, either previously untapped or unvalued
3. the development of industries in locations that use to be peripheric (which links directly to "central place"...)