Editor’s Note: This story accompanies the May 2016 issue of National Geographic magazine ... In the lower 48, where migration routes were unrecognized and fragmented by human settlement ...

This story appears in the July 2019 issue of National Geographic magazine ... missions to create the February 1969 hand-­painted map—considered the best reference at the time.

Gilbert H. Grosvenor, National Geographic magazine’s founding editor, is credited with saying: A map is the greatest of all epic poems. Its lines and colors show the realization of great dreams.

This story appears in the November 2010 issue of National Geographic magazine. Animal migration is a phenomenon far grander and more patterned than animal movement. It represents collective travel ...

But thanks to the amazing work of anthropologists and paleontologists like those working on National Geographic's Genographic Project, we can begin to piece together the story of our ancestors.

This story appears in the September 2019 issue of National Geographic magazine ... However, tracking migration through surveys, like an official census, is costly and can take years to complete.