This is known as a "Gravity Model" in the transportation literature and it's very far form being a new discovery. It's been around since the 1930s under various

This is known as a "Gravity Model" in the transportation literature and it's very far form being a new discovery. It's been around since the 1930s under various guises (https://en.wikipedia.org/wiki/Gravity_model_of_trade https://en.wikipedia.org/wiki/Gravity_model_of_trade) We used the same concept in our 2009 paper (https://www.pnas.org/content/106/51/21484 https://www.pnas.org/content/106/51/21484) but the exact functional form of the distance dependency (1/r, 1/r^2, 1/e^r, etc) varies with their exact definition of city due to the Modifiable Areal Unit problem (https://en.wikipedia.org/wiki/Modifiable_areal_unit_problem https://en.wikipedia.org/wiki/Modifiable_areal_unit_problem). In our specific case (cities defined as Voronoi cells centered around airports) the dependency was exponential.