http://www.fao.org/docrep/004/y1669e/y1669e0c.htm
http://link.springer.com/article/10.1007/s10806-012-9392-0
http://sites.duke.edu/foodbarriersinnc2013/results/spatial-analysis/
http://www.fao.org/docrep/004/y1669e/y1669e0c.htm
http://link.springer.com/article/10.1007/s10806-012-9392-0
http://sites.duke.edu/foodbarriersinnc2013/results/spatial-analysis/