@techreport{Willekens1978,
author = {Willekens, F. and Rogers, A.},
title= {Spatial population analysis: methods and computer programmes. Research Report RR-78-18},
year = {1978},
URL = {http://www.iiasa.ac.at/publication/more_RR-78-018.php
%[21 March 2014},
publisher = {International Institute for Applied Systems Analysis},
address = {Laxenburg, Austria},
}