Thin Plate Spline for phase 3 of an epidemic HPAI subtype H5N1 outbreaks in Romanian poultry, 2005–2006. The color scale represents the interpolated outbreak day, with dark blue being the earliest outbreak day and dark red representing the final days of each phase. The arrows show the estimated direction and rate of spread, with longer arrows corresponding to a slower rate of spread. The lack of uniformity in the surface suggests an epidemic originating in the center of the region, followed by rapid expansion in multiple directions occurring over a relatively short period of time. Note that the arrows vary markedly in both length and orientation. Clusters of small arrows represent local rapid spread and long arrows indicate slower disease spread, frequently occurring in disparate locations on similar epidemic dates.