Global Migration Maps. This is the first time I actually saw migration visualized, most likely due to data limitations. 

Migrations of people have existed for millennia and occur at a range of scales and time-periods (from small-scale journeys to work through to intercontinental resettlement). As a geographer I have long been interested in these and thought it was about time I mapped them! Using data from the Global Migrant Origin Database (thanks Adam for the tip) and R, my favourite stats software, I have produced the maps you see here (click on them for higher resolution). Each line shows the origins and destinations of at least 4000 people in a given year (2000 in this case). The more red the line the more people it represents. I have used great circle distance to plot them onto the Earth.  The map below shows the same magnitude of flows but just for Europe. The Earth has been flattened for this one so the flows are represented by arbitrary arcs.

Some caveats though.

Firstly they are based on a dataset where many of the movements are best guesses rather than measured data. You can read more about this here. It would also be great to have actual flows rather than inferred flows based on the number of migrants in each country. If I made these maps again I might draw lines between capital cities or population centres to avoid the impression that the majority of migrations to/ from Russia start/end in Siberia for example.

Today's TechCrunch article points to visa restrictions as the cause of high skill return migration in the Silicon Valley.

NBC Nightly News anchor Tom Brokaw visited Silicon Valley last month to meet immigrant entrepreneurs. At Microsoft’s Mountain View campus, he met with a dozen of them. More than half said that they might be forced to return to their home countries. That’s because they have the same visa issues that Kunal Bahl had. Unable to get a visa that would allow him to start a company after he graduated from Wharton in 2007, Kunal returned home to India. In February 2010, he started SnapDeal—India’s Groupon. Instead of creating hundreds of jobs in the U.S., Kunal ended up creating them in New Delhi.