Where more than one survey was conducted within a short time period, district level prevalence estimates were averaged. Districts were matched to corresponding shapefiles after being imported into the mapping software Arc Map 9.3 (ESRI, Redlands, CA, USA).
District estimates of prevalence were categorized according to WHO prevalence thresholds used to denote treatment requirements. TRA data were classified to show the presence or absence of trachoma. An additional category was included for active trachoma when over 10% of children examined were graded positive.