Fig. 4

United States region migration rates and count heat map, 2005–2016. Statistically supported migration rates (BF > 3.0) of class I (a) and class II (b) viruses among regions of the United States are represented by arrows with width proportional to median migration rate per year. In the heat maps of class I (c) and class II (d) viruses, darkness of each cell is proportional to the absolute number of transitions from the first column into the second column over the most recent 12 years of data. (AK – Alaska, MW – Midwest, NE – Northeast, P – Plains, S – South, W- West, X – Outside United States). Base map was used with permission from OpenStreetMap (https://www.openstreetmap.org/copyright)