To report a multipart visual series on border barriers around the globe, we drove the entire length of the U.S.-Mexico border — from Brownsville, Tex., to San Diego, with crossings into Mexico scattered throughout — talking to locals and experts about President Trump’s promise to build the wall.

Trump’s action to start construction leaves unclear whether the administration will build a wall along the entire border or just in certain areas.

Below are five notable challenges to building the wall that we observed along the journey.

President Trump has promised to build a wall on the U.S. Mexico border. People living along the border say there will be significant challenges. (Zoeann Murphy/The Washington Post)

1. The terrain is very rough in some areas

UNITED STATES

Sonoran

Desert

Big Bend

National

Park

Amistad

Dam

Chihuahuan

Desert

MEXICO

UNITED STATES

California

Arizona

New Mexico

Texas

140 miles of border

372

179

1,241

El Paso, Tex.

Big Bend

National

Park

Amistad

Dam

Sonoran Desert

San Diego,

Calif.

Chihuahuan

Desert

Brownsville,

Tex.

Baja California

Sonora

Chihuahua

Coahuila

Nuevo

Leon

MEXICO

Tamaulipas

UNITED STATES

California

Arizona

New Mexico

Texas

140 miles of border

372

179

1,241

El Paso, Tex.

Amistad

Dam

Big Bend

National

Park

Sonoran Desert

San Diego,

Calif.

Chihuahuan

Desert

Brownsville,

Tex.

Baja California

Sonora

Chihuahua

Coahuila

Nuevo

Leon

Tamaulipas

MEXICO

The nearly 2,000-mile border features a variety of climates, vegetation and terrain. Most of the current border fence exists west of El Paso, Tex., where the border switches from relatively straight lines to the winding path of the Rio Grande.

On its way to the Gulf of Mexico, the river cuts through the mountains of Big Bend National Park and rests in reservoirs, including near Amistad Dam. Both present clear challenges to wall builders.

The Rio Grande, as seen from the border crossing at the Amistad Dam near Del Rio, Tex. The land on the left of the river is the United States; on the right is Mexico. (Zoeann Murphy/The Washington Post)

Byron Hedges, a local who has fished in the Amistad Dam, said he thought the topography would make construction difficult. He said, “If Donald Trump went and flew the whole border, just in Texas, he would realize it’s infeasible. It’s too rough of country.”

[ Why Trump can’t simply build a wall along the U.S.-Mexico border with an executive order]

2. Unlike the Western border states, most of Texas is privately owned

A significant amount of border land in Arizona and New Mexico is owned by the federal government. But most Texas land is privately owned, thanks to its terms of entry into the Union 200 years ago.

Segments with some kind of fence

Segments with no fence

Federal land

CA

U.S.

NM

AZ

S.Diego

El Paso

Nogales

TX

Tijuana

C. Juarez

Del Rio

Laredo

Brownsville

100 miles

Federal land

CALIFORNIA

Segments with fence

Segments with no fence

ARIZONA

San Diego

NEW

MEXICO

El Paso

Tijuana

Nogales

TEXAS

Ciudad

Juarez

Nogales

BAJA

CALIFORNIA

CHIHUAHUA

SONORA

Del Rio

Eagle Pass

Laredo

COAHUILA

100 miles

Brownsville

NUEVO LEON

Matamoros

This difference led to lawsuits between Texans and the federal government during construction of the fencing that exists today.

According to a project on the border barrier by the University of Texas’s law school, the United States sued “hundreds of private property owners to obtain title to their land to allow for construction of segments of the wall on that land.” Resuming barrier construction on private lands will likely invite more lawsuits and logistical challenges.

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3. Most of the border is natural, but a human-made barrier is not

The southern border of Texas is technically somewhere in the middle of the Rio Grande. The river has changed course in the past, creating boundary disputes between the United States and Mexico.

The existing border fencing in southern Texas often sits far from the river, outside its flood plains — creating wide seams between the fence and the official border.

Some Americans live on the Mexican side of the border fence.

River Bend Resort, a golf course and residence in Brownsville, Tex., sits between a gap in the existing fence. If the wall were completed, based on U.S. regulations, it would bisect the property, according to owner Jeremy Barnard. Roughly 200 residents and 15 of the 18 golf holes would sit south of the border wall.

“What is the government’s plan? Are they going to come and buy out 200 people of their houses?” he said. “There’s so much more to it than ‘let’s just build a wall.’ ”

1,500 feet

1,500 feet

1,500 feet

4. Surveillance makes the barrier effective

Security experts say that border barriers are merely obstacles to would-be crossers unless they are watched. Former homeland security secretary Janet Napolitano famously remarked, “You show me a 50-foot wall, and I’ll show you a 51-foot ladder.”

Fencing is just one part of the effort by U.S. Customs and Border Protection to secure the country’s borders. The number of Border Patrol officers has doubled in recent years. Checkpoints strategically line roads along the border. Where no fencing exists, cameras and sensors do.

Efforts to build a “virtual fence” to supplement the physical barrier have proven challenging. SBInet, an initiative to augment border patrol agents with advanced technology, struggled to meet deadlines and faced repeated technical problems before it was terminated in 2011, according to a recent Congressional Research Service report.

[ Trump Promise Tracker]

NOGALES,

ARIZ.

 

Pedestrian fence, 21 feet

The original Nogales pedestrian fence was built more than 100 years ago to hold back cattle. The latest 21-foot fence, separating Nogales, Mexico, from Nogales, Ariz., went up in 2011. People still manage to climb over it with ladders and rope. The Nogales section of the fence extends for some miles on either side of the town. In total, there are 123 miles of pedestrian fence in Arizona.

Car fence, 8 feet

Outside Nogales, a vehicle barrier picks up where the pedestrian fence ends, but it too eventually runs out. In total, there are 183 miles of vehicle fence in Arizona.

NOGALES,

ARIZ.

 

Pedestrian fence, 21 feet

Car fence, 8 feet

Outside Nogales, a vehicle barrier picks up where the pedestrian fence ends, but it too eventually runs out. In total, there are 183 miles of vehicle fence in Arizona.

The original Nogales pedestrian fence was built more than 100 years ago to hold back cattle. The latest 21-foot fence, separating Nogales, Mexico, from Nogales, Ariz., went up in 2011. People still manage to climb over it with ladders and rope. The Nogales section of the fence extends for some miles on either side of the town. In total, there are 123 miles of pedestrian fence in Arizona.

NOGALES, ARIZ.

 

Pedestrian fence, 21 feet

Car fence, 8 feet

The original Nogales pedestrian fence was built more than 100 years ago to hold back cattle. The latest 21-foot fence, separating Nogales, Mexico, from Nogales, Ariz., went up in 2011. People still manage to climb over it with ladders and rope. The Nogales section of the fence extends for some miles on either side of the town. In total, there are 123 miles of pedestrian fence in Arizona.

Outside Nogales, a vehicle barrier picks up where the pedestrian fence ends, but it too eventually runs out. In total, there are 183 miles of vehicle fence in Arizona.

5. Migrants are determined and often have few options

Increased violence in some Central American countries has pushed migrants and asylum seekers to the U.S. at a breakneck pace. Apprehensions of unaccompanied children from El Salvador, Guatemala and Honduras have doubled in the past three years, according to Border Patrol figures.

Apprehensions of unaccompanied

children by country

2016

MEXICO

11,926

2013

MEXICO

17,240

EL SALVADOR

17,512

EL SALVADOR

5,990

GUATEMALA

18,913

GUATEMALA

8,068

HONDURAS

6,747

HONDURAS

10,468

Apprehensions of unaccompanied children by country

MEXICO

EL SALVADOR

GUATEMALA

HONDURAS

17,240

5,990

8,068

6,747

2013

2016

MEXICO

EL SALVADOR

GUATEMALA

HONDURAS

11,926

17,512

18,913

10,468

Apprehensions of unaccompanied children by country

MEXICO

EL SALVADOR

GUATEMALA

HONDURAS

17,240

5,990

8,068

6,747

2013

2016

MEXICO

EL SALVADOR

GUATEMALA

HONDURAS

11,926

17,512

18,913

10,468

UNHCR reported that asylum seekers from those three countries have increased fivefold since 2012.

Ramon Reyes, a Guatemalan migrant in Reynosa, Mexico, recounted tragic stories of war, corruption and murder in his home country. He said he left because of the violence and a lack of  jobs.

“Look, my opinion about fences, about those obstacles they’re placing, is that, no. No matter how many barriers they may place, they won’t stop us.”

In Reynosa, Mexico, a town that borders the Unites States, Mexicans and others living there share their thoughts on President Trump’s push to build a wall. (Zoeann Murphy/The Washington Post)

Sources: Google Earth, United States Geological Survey, Center for Investigative Reporting, Openstreetmap.org, Customs and Border Protection, UNHCR. Published Jan. 25, 2017.

Note: A previous map incorrectly labeled two Texas towns. It has been corrected.

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