Spatial variation of a) W. bancrofti and b) P. falciparum in parts of Urim and Urat census districts, East Sepik Province. The scale is in kilometres with an arbitrary origin near the centre of the study area (142.7°E, 3.6°S). Each hexagon represents one hamlet, with the shading showing the quartile of the standardized parasite density ratio. For W. bancrofti, the 0, 25, 50, 75 and 100th percentiles are 0.27, 0.56, 1.02, 1.71 and 4.3 respectively. For P. falciparum they are 0.43, 0.94, 1.27, 1.80 and 11.64. The curve plotted against the vertical axis shows the rate at which correlation in mean parasite density decays with distance. The solid lines in the body of the map show unpaved roads, and the dashed line indicates the division of villages between the two census districts.