@inbook{Isard1998,
author = {Isard, W.},
title= {Gravity and spatial interaction models},
year = {1998},
editor = {Isard, W.},
editor = {Azis, I.J.},
editor = {Drennan, M.P.},
editor = {Miller, R.E.},
editor = {Saltzman, S.},
editor = {Thorbecke, E.},
booktitle = {Methods of interregional and regional analysis},
address = {Cambridge},
publisher = {Ashgate Publishing Limited},
pages = {243--280},
}