I am interested in the idea that natural transportation networks could be an important factor in explaining the hierarchy of ancient cities. However, I have a question about the regression model (12) which has the variables CropYield and Roads. Agricultural suitability and natural transportation networks could be correlated in some cases. When a location has good agricultural suitability, people are more likely to live there, so there would be more transportation networks around this area. As presented in the paper, the correlation between CropYield and the estimates of ancient city sizes would not be significant when controlling for natural road score. Therefore, would the potential correlation possibly lead to the insignificance? I would appreciate it if there is more explanation on this model and the results.
I am interested in the idea that natural transportation networks could be an important factor in explaining the hierarchy of ancient cities. However, I have a question about the regression model (12) which has the variables CropYield and Roads. Agricultural suitability and natural transportation networks could be correlated in some cases. When a location has good agricultural suitability, people are more likely to live there, so there would be more transportation networks around this area. As presented in the paper, the correlation between CropYield and the estimates of ancient city sizes would not be significant when controlling for natural road score. Therefore, would the potential correlation possibly lead to the insignificance? I would appreciate it if there is more explanation on this model and the results.