'Exodus' from Puerto Rico: A visual guide

Updated 1743 GMT (0143 HKT) February 21, 2018

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(CNN)Before Hurricane Maria hit Puerto Rico on September 20, there already was an unprecedented migration from the Caribbean island to the mainland United States -- at least in part because of the US commonwealth's financial crisis. After the storm, academics are starting to use words such as "exodus" and "stampede" to describe the massive outflow of people.

"This is the greatest migration ever from Puerto Rico since records have been taken," said Jorge Duany, a professor of anthropology at Florida International University.
Some reasons for the migration are obvious: Millions of Americans living in Puerto Rico were left without power or running water because of the Category 4 hurricane. Schools were closed. Jobs lost. There seemed to be little hope on the horizon. Puerto Ricans are American citizens and can move to the states without visas or other paperwork. And so, many did.
Yet the scope and shape of this diaspora remain mysterious.
So far, estimates of its size have been based on airline traveler data, which some academics consider unreliable because flying off the island doesn't necessarily mean you're going to migrate. Florida school enrollment numbers have added clarity, but they only cover students who showed up in the Sunshine State, not the entire nation.
To get a clearer picture of the migration patterns, CNN analyzed data from two federal government agencies obtained under the US Freedom of Information Act.