A hundred years ago, in his notion of cultural geography, Carl Sauer had extended Herbert Spencer's consideration of mind–environment interaction, alluding to a spatio-temporal continuum in which changes through human intervention in the physical environment feed back onto human cognition, only to result, yet again, in next round of environmental change that feeds back onto cognition. Independent of Sauer, Walter Benjamin, had pointed out that the same feedback process occurs between the built environment and minds within it.