Space–time variography for malaria proportion. Plots shown are (a) sample space–time variogram surface, (b) sample spatial variogram (circles) with fitted 1-D model (line), (c) sample temporal variogram (circles) with fitted 1-D model (line), and (d) 2-D product–sum space–time variogram model. Each vertical axis measures the semivariance, γ, and horizontal axes measure either spatial lag (hs) or temporal lag (ht).