This is a cool map and there's tons of information in it. It'd be nice to see more details, like the actual numbers instead of just a top 3 counties list. Or if I pause the timeline and hover over a country it'd be neat if it listed that year's exodus.

Why do come countries brighten in some years but then dim later on?

Edit: ah I see the associated blog post has a little more info, especially about the brightness question. http://metrocosm.com/animated-immigration-map/