Agreed. For me, arrows would be better to imply movement. Specifically, arrows going from city with the lightness/darkness (tone?) indicating how many are going where. Circles just don't connect with the data part of my brain very well. It's hard to compare the area of circles to gauge just how much bigger one is than the other.
But forbes probably had a team of people working on theirs for a few afternoons at least.
But forbes probably had a team of people working on theirs for a few afternoons at least.