Puerto Rico 'exodus': How CNN analyzed and mapped the data

Updated 1745 GMT (0145 HKT) February 21, 2018

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(CNN)For its story and graphics showing where Puerto Ricans may have migrated after Hurricane Maria, CNN analyzed two national data sets obtained under the Freedom of Information Act:

Individual assistance applications

The FEMA data, which captured 1,057,006 applications through November 11, included ZIP codes for each applicant's current mailing address and "damaged dwelling." An early analysis of the data found thousands of entries where ZIP codes were either invalid or indicated a damaged property location outside Puerto Rico.
FEMA officials told CNN these errors occurred because ZIP codes are "a required field that is entered by the registrant" when they apply for assistance and "it is possible that registrants do not know their ZIP code, and therefore enter any value as the f