Before revision:  In many-region geography, the network structure of social proximity emerges as the determinant of the geographical distribution of workers when trade becomes freer. If social proximity is governed by geographical distance (as in ground transportation) , a mono-centric concentration emerges .
After revision:  In many-region geography, the network structure of social proximity emerges as the determinant of the geographical distribution of workers as economic integration increases. If production externalities are governed solely by geographical distance (as in ground transportation) , a mono-centric concentration emerges .