March 4, 2016
By James Whitlow Delano

The candidates for president of the United States, (click here) particularly on the Republican side, have hotly debated how to handle the roughly 2,000-mile (3,200-kilometer) border between the United States and Mexico.

Donald Trump has famously and repeatedly promised to seal the border with a wall if he's elected. He and others have promised to send people who illegally crossed the border—a number that appears to have leveled off—back to Mexico. For these people, the border wall isn't an abstraction. Many parts of the border are already covered in fences. In other spots, the wall is not made of bricks, but out of scanners, drones, and guards....

This has been an ongoing project for "National Geographic."

January 25, 2017
By Daniel Stone

President Trump ordered the construction today of a border wall (click here) along the U.S.-Mexico border. But there's at least one complication so far: a wall already exists in some areas. Last spring, we visited different parts of border—the ones heavily guarded with long lines for cars to cross, and the places where the two countries are separated by little more than dirt and trees.

The border that Trump hopes the wall will protect is roughly 2,000 miles long. And the area spans diverse geology, including terrain not always hospitable or conducive to large-scale construction. (Trump hasn't said exactly how high he wants the wall to be, or how thick, although engineering and media critiques have questioned the feasibility of such a project.)...