Figure 2

Prevalence of T. parva in Tororo District; September to December 2011. Shows the spatial distribution of T. parva in Tororo district between September and December 2011 interpolated using 22 point prevalences in the 22 study villages to create a district wide spatial effect. An inverse distance weighted interpolation on the analyst extension of ArcMap 10.1 was used to generate a continuous T. parva prevalence map on a red colour ramp. Parameters were set so that for each pixel in the continuous raster an average prevalence was calculated based on all prevalence values at village level. Being a weighted average, the weight is higher for villages near the pixel and lower for more distant villages. A default exponent value of 2 was chosen such that each pixel value was taken to be the sum of observed prevalence values, which were first divided by the squared distance between villages. The result was then divided by the number of observations and multiplied by the sum of distances to generate a continuous T. parva prevalence map over the 22 individual point prevalences.