1. Bertin, J., J.J. Hémardinquer, M. Keul, and W.G.L. Randies. 1971. Atlas of food crops. Geographical and chronological survey for an atlas of world history. École Pratique des Hautes études-Sorbonne. VIe Section: Sciences économiques et Sociales. Centre de Recherches Historiques et Laboratoire de Cartographie, Paris, France.
2. Carter, S.E., L.O. Fresco, and P.G. Jones, with J.N. Fairbairn. 1992. An atlas of cassava in Africa. Historical, agroecological and demographic aspects of crop distribution. Centro Internacional de Agricultura Tropical, Cali, Colombia.
3. CIESIN. 2000. Global gridded population database. Available at http://www.ciesin.org/
4. Corbett, J.D., and R.F. O’Brien. 1997. The spatial characterization tool - Africa v 1.0. Texas Agriculture Experiment Station, Texas A&M University System, Blackland Research Center Rept #97-03, CDROM Publication.
5. Situation and outlook series;F.W. Crook,1993