With the border between the U.S. and Mexico being as huge as it is (and it's pretty huge), it should come as a surprise to absolutely nobody that some parts of the border that are heavily populated in Mexico will stand opposed to a literal desert in the U.S. and vice versa. The two countries are just way too big to have a city occupying every square inch of them.
That being said, it is pretty crazy to see just how much of a difference there is between the two countries. Aerial pictures are pretty neat, aren't they? They sure are.