Flow Map

http://scitechdaily.com/how-airports-will-influence-the-spread-of-a-contagious-disease/

Flow maps are developed in cartography to show linear movement from one location to another with the width of the flow line increasing or decreasing depending on quantity. The flow map above shows the flight routs from the 40 largest U.S. airports. This type of map can be extremely helpful in determining links to how things spread, such as disease, and determining the place of origin.