'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.
Together, the data sets from the Federal Emergency Management Agency and the US Postal Service show Puerto Ricans appear to have migrated to all 50 US states in the aftermath of Maria.
As of November 11, FEMA received at least 10,600 applications for disaster assistance from ZIP codes in 50 states and Washington, according to FEMA data provided to CNN.
The applications may represent households, not individual people. The average Puerto Rican household is made up of about three people, according to the US Census Bureau.
In total, FEMA received more than 1 million applications for aid related to Hurricane Maria in Puerto Rico -- indicating nearly everyone who asked FEMA for help under its Individual Assistance programs did not leave the island after the storm.
Still, the data appear to show a substantial increase in the outflow of people from Puerto Rico.
"It sounds possible that we're on pace for a historic net outmigration to the US" from Puerto Rico, said Jens Manuel Krogstad, an editor at the Pew Research Center. "In 2015, the net outmigration was about 64,000 people. And so, from the numbers you described, it sounds like it's possible that even after just a few months we're already on pace to overshoot that."
Separately, between October 1 and December 31, the US Postal Service received at least 6,590 change-of-address requests -- nearly five times the amount received during the same months the previous year -- from Puerto Rico and the US Virgin Islands to the 50 states and District of Columbia. The Postal Service received about 2,900 additional requests to change addresses within Puerto Rico, according to the data, suggesting that while some people left Puerto Rico, others moved within the storm-battered island.
Neither data source is a precise measurement of hurricane-related migration. It's possible that some people changed their addresses for reasons unrelated to Hurricane Maria. FEMA applicants could have listed current addresses in the states for reasons other than migration. They may have listed a relative's address in the states even if they did not move away from Puerto Rico, a FEMA representative said.
Several demographers and disaster experts said these methods of counting -- tracking disaster-assistance claims and official changes of a