Spatial distribution of predictor variables.

Predictor variables included the number of poultry (chicken and duck) houses, the density of chicken houses per km², the density of duck houses per km², the density of fattening duck (all stages) houses per km², the density of fattening duck (breeding stage) houses per km² and the density of fattening duck (force-feeding stage) houses per km². Shapefiles used to create maps are based on administrative boundaries available in the public domain (CC BY 4.0). (PDF)