¡Viva La Diferencia!
The international border running between Mexico and the United States represents more than just a cultural divide. Along the 3,169 km (1,969 mi) border there exist stark geographical differences as well, illustrated by these photos from 2007.
Above, a deep perspective image shows what amounts to be a rather small fence separating the San Diego, California Sector of the United States (left) with Tijuana, Mexico.
Below, residents of Naco, Arizona and Naco, Mexico overcome boundaries and join up for an international game of volleyball during the fourth "Fiesta Bi-Nacional".
According to the International Boundary and Water Commission, an estimated 350 million people legally cross every year. As for illegal crossings, estimates place the number at 500,000 but for every successful cross, imagine the number that didn't.