引力模型中如何确定两国间距离

The basic idea, inspired by Head and Mayer (2002), is to calculate
distance between two countries based on bilateral distances between the biggest cities of those
two countries, those inter-city distances being weighted by the share of the city in the overall
country’s population.
这里的意思是用两个国家间最大的城市距离来比较，那么中国用上海这个城市，其它国家用各自的最大城市（经济规模上）或者说经济中心。这样可以吗？求解答！！