“Isn’t it so fascinating that the simple act of drawing a line on a map can transform the way we see and experience the world?” Ronald Rael observes in the opening of the documentary film “Borderlands,” which looks at communities in San Diego and Tijuana, Brownsville and Matamoros, and El Paso and Juárez. Rael, an architect, explores the area near the border fence outside El Paso with an eye tuned to reimagining the space around him and plotting ways to transgress it. He is accompanied by his nine-year-old son, Mattias, and he teaches the boy how to interpret a wall that has come to dominate the political conversation in the United States.

Rael is well aware that, not too long ago, the boundary between the United States and Mexico, which is now delineated by more than seven hundred miles of fencing, was an open frontier, dotted with stone monuments. His book “Borderwall as Architecture” makes clear that the billions of dollars the U.S. government has spent on curbing migration and enhancing border security have done little to deter those intent on crossing by foot, using wooden ladders and ramps, or through tunnels. Decades of flawed policies suggest that the building of a grand wall is entirely divorced from the reality on the ground.

“Borderlands” attends to many realities that are often ignored in Washington. Rael embodies one such reality. Ana Eguiarte, an environmentalist in Tijuana, and Mauricio Ibarra, a city planner in Brownsville, offer their own lenses through which to view life in the region. Eguiarte is working to reduce the flows of trash into the Tijuana River Estuary. We meet her in a classroom, where she asks children if they know what happens to garbage when it rains. “Se mueve!” (“It moves!”) they all respond in unison. An explanation follows: garbage travels freely between the two sides, posing an environmental threat that can be addressed only if both countries work together.

Ibarra’s routine, meanwhile, straddles the cities of Brownsville, Texas, and Matamoros, Mexico. He is one of twelve thousand people who cross the border between the two cities daily. Long, slow lines of cars wait to cross the bridge over the Rio Grande. Ibarra and his team are advocating for the creation of a bike lane, which could replace abandoned train tracks. The plan would not only allow commuters and visitors to move around seamlessly; it would also ease traffic for drivers. The final hurdle is getting the border authorities to green-light their case for mobility.

Where there once was an imaginary line, there are now steel beams, reinforced with razor wire and as many as three layers of barriers. The U.S. started installing border fences in the early nineties, and, in the past decades, the wall has only grown taller and longer—separating everything along its way, including rivers and Native American territories, cultural sites and universities, people’s homes and wildlife preserves.

What some see as a means of protection has actually sundered two communities with a shared past, present, and future. When we see Rael’s interactions with people on the Mexican side of the fence (helped along by his own creativity), it becomes clear that, for people like him, Eguiarte, and Ibarra, whose lives have been shaped by the border, the wall is nothing but an obstruction. They will continue looking beyond it.