Before revision:  If social proximity is governed by geographical distance (as in ground transportation) , a mono-centric concentration emerges . If geographically distant pairs of regions are ``socially close'' (due to, e.g., passenger transportation modes with strong distance economy such as regional airlines), then geographically multi-centric spatial distribution can be sustainable.
After revision:  If social proximity is governed by geographical distance (as in ground transportation) , a mono-centric spatial distribution emerges in the form of suburbanization. However, if geographically distant pairs of regions are ``socially close'' (due to, e.g., passenger transportation modes with strong distance economy such as regional airlines), then geographically multi-centric spatial distribution can be sustainable.