影像來源/ SOURCES: "QUANTIFYING GLOBAL INTERNATIONAL MIGRATION FLOWS," BY GUY J. ABEL AND NIKOLA SANDER, IN SCIENCE, VOL. 343; MARCH 28, 2014; "THE GLOBAL FLOW OF PEOPLE," BY NIKOLA SANDER, GUY J. ABEL AND RAMON BAUER www. global-migration. info; GRAPHIC BY NIKOLA SANDER