The subdistrict (an administrative unit covering an average area of 69.7 km 2 , called ''Tambon'' in Thaï) was used as the spatial scale of interest for the study. Out of the 7 408 subdistricts in Thailand, we excluded from the analysis those located on islands since we assumed that they played a minor role in disease distribution. This resulted in a geo-database of 7 366 subdistricts which we considered as the statistical units for the analysis.