Fig. 2.

Network model of COVID-19 spreading across the United States. Discrete graph $\mathcal{G}$ of the United States with $N=50$ nodes and the 200 most travelled edges. Size and color of the nodes represent the degree $D_{\mathit{II}}$, thickness of the edges represents the adjacency $A_{\mathit{IJ}}$ estimated from annual incoming and outgoing passenger air travel