Andrew J. Tatem holds a joint appointment as a researcher@the Spatial Ecology and Epidemiology Group of the Department of Zoology@the University of Oxford, and as a research associate@the Centre for Geographic Medicine in Nairobi, Kenya. He received his Ph.D. in 2001 jointly from the Departments of Electronics and Computer Science and Geography@the University of Southampton. Address: Spatial Ecology and Epidemiology Group, Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, UK. Internet: andy.tatem@zoo.ox.ac.uk