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Distribution of the density of domestic pig farms, wild boar and free-ranging pigs, expressed as number/km2, by indoor and outdoor farms. Features were collected based on 10 km2 radius around each epidemiological unit (i.e., outbreak farm). Statistically significant differences between indoor and outdoor farms are identified by a p-value <0.0001 (***), or p-value between 0.05–0.0001 (**).
