@article{Huff2015,
author = {Huff, D.L. and Jenks, G.F.},
title= {A graphic interpretation of the friction of distance in gravity models},
year = {2015},
doi = {10.1111/j.1467-8306.1968.tb01670.x},
URL = {https://doi.org/doi:10.1111/j.1467-8306.1968.tb01670.x},
volume = {58},
number = {4},
pages = {814‒824},
}