Two AFP photographers are documenting life on each side of the US-Mexico border. Jim Watson is travelling along the US side of the border, while his colleague Guillermo Arias is making the same journey on the Mexican side. IBTimes UK presents photos from the first four days of their travels, from San Diego to Nogales.

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13 February 2017: AFP photographers Jim Watson (L) in San Diego, California, and Guillermo Arias (R) in Tijuana, Mexico are seen at the US/Mexico border fenceJim Watson/AFP

US President Donald Trump has ordered the construction of a multibillion-dollar "great wall" along the roughly 2,000-mile (3,200km) US-Mexico border, a project that could cost as much as $21.6 billion (£17.4bn), and take more than three years to construct. About one-third of the length of the border is already fortified with tall fencing.

San Diego used to be the busiest corridor for illegal immigration until the mid-1990s, when a surge in agents and fencing pushed traffic to Arizona. The city has one of the most fortified stretches of border, with razor wire atop much of its fencing with Mexico.

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13 February 2017: A man works out on the beach in Playas de Tijuana in northwestern Mexico, next to the Mexico-US border fenceGuillermo Arias/AFP
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13 February 2017: People in Tijuana, Mexico, look into San Diego over the border fence separating the beaches at Border Field State ParkJim Watson/AFP
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13 February 2017: A bird runs through the surf at Border Field State Park in San Diego, CaliforniaJim Watson/AFP
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13 February 2017: A stream of tail lights illuminate the road as cars cross the border into Mexico from San DiegoJim Watson/AFP
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13 February 2017: People cross a bridge in Playas de Tijuana, Mexico, with the Tijuana Estuarine Research Reserve in San Diego in the backgroundGuillermo Arias/AFP
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13 February 2017: Taxi drivers wait outside the San Ysidro Port of Entry in San Diego, CaliforniaJim Watson/AFP
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13 February 2017: Municipal Police patrol the area around a money exchange in Tijuana, Mexico, near the US/Mexico borderJim Watson/AFP

The United States does not have a way to measure how well fencing works to deter illegal crossings from Mexico, according to a report released by Congress' main watchdog. Border Patrol leaders have struggled to say with any degree of precision how well fences work, in part because it's unknown how many people get away. Another unknown is the extent to which fences or other factors such as the number of agents explain why people are caught.

Few people dispute that fences contributed to a sharp drop in crossings in cities like San Diego and El Paso, Texas, where people can easily blend in once they enter the country. However, holes are often cut into fences in isolated areas. Some 9,287 breaches were reported in pedestrian fencing from 2010 to 2015. Agents said crossers have built ramps to drive over fences in Arizona and have burrowed beneath them.

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14 February 2017: An abandoned sofa sits against the border fence on the US/Mexico border in Tecate, CaliforniaJim Watson/AFP
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14 February 2017: Border Patrol Agent Barona checks out the area after receiving a call of seismic activity on a trail near the US/Mexico border in Tecate, CaliforniaJim Watson/AFP
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14 February 2017: A donkey grazes on the Mexican side of the border, as seen from Tecate, CaliforniaJim Watson/AFP
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14 February 2017: A Guadalupe Virgin altar is pictured next to the crossing port at the US-Mexico border in Tecate, northwestern MexicoGuillermo Arias/AFP
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14 February 2017: A cross in honour of fallen border patrol agents stands near the border fence in Tecate, CaliforniaJim Watson/AFP
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14 February 2017: A section of the border fence in reflected in the side mirror of a vehicle in Tecate, CaliforniaJim Watson/AFP
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14 February 2017: A section of the border fence ends and stands open in Tecate, CaliforniaJim Watson/AFP
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14 February 2017: A promotional banner of a local farm uses image of President Donald Trump and the wall to promote their products, on the outskirts of Tecate in northwestern MexicoGuillermo Arias/AFP
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14 February 2017: Jose Lopez, a driver from Honduras, shows his passport at La Rumorosa in northwestern Mexico, near the US/Mexico borderGuillermo Arias/AFP
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14 February 2017: Street vendors use the border fence as shelves to display their items, in Mexicali, northwestern MexicoGuillermo Arias/AFP
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14 February 2017: A stuffed animal rests next to a brick inscribed with the words 'John Doe' in an unmarked dirt lot at the end of Terrace Park Cemetery in Holtville, California, where the remains of hundreds of unidentified migrants are buriedJim Watson/AFP
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14 February 2017: A woman works at a roadside shop along the Mexican side of the border fence, as seen from in Calexico, CaliforniaJim Watson/AFP
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14 February 2017: A band plays to traffic on the Mexican side of the border fence, as seen from Calexico, CaliforniaJim Watson/AFP

Border patrol officials have noticed a trend of Central American migrants turning themselves into US officials when they cross overland from Mexico in the hope that they may stay on in the United States. Ruben Garcia, the director of Annunciation House, a Roman Catholic charity in El Paso, Texas, that gives shelter to migrant families, told Reuters no border wall will stop this. "All the border walls are not going to stop people walking right into ports of entry and turning themselves in so I'm not sure," he said.

Because most of the families are from Central America, they cannot immediately be turned around and sent back to Mexico. A Reuters review of US Customs and Border Patrol data shows an accelerating trend of Central American families who hand themselves in at the border and are released while awaiting deportation or a decision on an asylum request. In the last three months of 2016, the number of people - almost all of them families and children - who handed themselves in to agents along the U.S.-Mexican border rose by a quarter versus the same period the year before, CBP data shows. Agents apprehended a total of 136,670 people crossing the Mexican border, the highest number since 2008, and 48 percent of those were unaccompanied children or families with children.

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15 February 2017: The shadow of a section of the US/Mexico border fence is seen at San Luis Rio Colorado, Sonora state, northwestern MexicoGuillermo Arias/AFP
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15 February 2017: A section of the US/Mexico border fence is seen at San Luis Rio Colorado, Sonora state, northwestern Mexico.Guillermo Arias/AFP
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15 February 2017: A woman walks next to a painting of former US President Barack Obama on the US/Mexico border fence in San Luis Rio Colorado, Sonora state, northwestern MexicoGuillermo Arias/AFP
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15 February 2017: Temporary agricultural workers walk off a lettuce farm at the end of their shift outside Yuma, ArizonaJim Watson/AFP
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15 February 2017: Temporary agricultural workers from Mexico return to the Port of Entry in San Luis, ArizonaJim Watson/AFP
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15 February 2017: A temporary agricultural worker looks out the window of a bus near the Port of Entry in San Luis, ArizonaJim Watson/AFP
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15 February 2017: Jose (only first name given) advertises a shop dressed as Uncle Sam on a corner in San Luis, ArizonaJim Watson/AFP
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15 February 2017: Cross bars make up the border fence along the Colorado River in Yuma, ArizonaJim Watson/AFP
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15 February 2017: Visitors from the United States walk past a dental practice in Los Algodones, northwestern Mexico, near the borderGuillermo Arias/AFP
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15 February 2017: Visitors from the United States sit near a souvenir stand and dental clinic in Los Algodones, northwestern MexicoGuillermo Arias/AFP
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15 February 2017: A Mexican national flag flies over a small shelter at a municipality rubbish dump at Los Algodones in northwestern MexicoGuillermo Arias/AFP
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15 February 2017: Rubbish collector Hector Manuel Anguiano, who was deported from the United States ten years ago, works at a municipality rubbish dump near the border, in Los Algodones, northwestern MexicoGuillermo Arias/AFP
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15 February 2017: A section of the US/Mexico border fence is seen at Los Algodones, northwestern MexicoGuillermo Arias/AFP
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15 February 2017: The Imperial Sand Dunes are seen near the US/Mexico border in Dunes, CaliforniaJim Watson/AFP
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15 February 2017: A section of the US-Mexico border fence runs through the Imperial Sand Dunes in Dunes, CaliforniaJim Watson/AFP
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15 February 2017: An old wheel chair sits in the middle of the desert near the border fence on the US/Mexico border in Winterhaven, CaliforniaJim Watson/AFP
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15 February 2017: A sign warns against swimming the All American Canal near the border fence on the US/Mexico border in Winterhaven, CaliforniaJim Watson/AFP
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15 February 2017: A construction crew works near the border fence on the US/Mexico border at the Imperial Sand Dunes in Dunes, CaliforniaJim Watson/AFP
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16 February 2017: A view of the the US/Mexico border fence at night in San Luis Rio Colorado, northwestern MexicoGuillermo Arias/AFP
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16 February 2017: Temporary agricultural workers tend a farm in the early morning in Weldon, ArizonaJim Watson/AFP
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16 February 2017: A tree grows through the border fence outside Lukeville, ArizonaJim Watson/AFP
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16 February 2017: Mexican soldiers drive along a section of the US/Mexico border fence in Sonoyta, northwestern MexicoGuillermo Arias/AFP
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16 February 2017: The border fence goes from large to just a waist high barrier near Lukeville, ArizonaJim Watson/AFP
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16 February 2017: A section of the border fence runs along a road outside Lukeville, ArizonaJim Watson/AFP
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16 February 2017: A section of the US/Mexico border fence is seen west Sonoyta, northwestern MexicoGuillermo Arias/AFP
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16 February 2017: The border fence is surrounded by cacti at Organ Pipe Cactus National Monument near Lukeville, ArizonaJim Watson/AFP
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16 February 2017: A sign warns against illegal smuggling in Organ Pipe Cactus National Monument near Lukeville, ArizonaJim Watson/AFP
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16 February 2017: A sign advertises the 'Gringopass' motel and RV park on the US/Mexico border in Lukeville, ArizonaJim Watson/AFP
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16 February 2017: A roadside memorial reading 'Soy Libre' (I am Free) stands by the roadside outside Lukeville, ArizonaJim Watson/AFP
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16 February 2017: Tyres used by US Border Patrol to grade the road so fresh tracks can be seen, lie near the border fence outside Lukeville, ArizonaJim Watson/AFP
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16 February 2017: A slipper made of carpet fabric, used to wrap migrants' shoes to hide foot prints, lies abandoned next to the border fence outside Lukeville, ArizonaJim Watson/AFP
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16 February 2017: Carpet shoe covers to hide footprints are displayed for sale among other goods for migrants crossing the desert, in Altar, northwestern MexicoGuillermo Arias/AFP
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16 February 2017: Backpacks and camouflage clothing are displayed for sale among other goods for migrants crossing the desert, at a local shop in Altar, northwestern MexicoGuillermo Arias/AFP
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16 February 2017: Deported migrants wait in a park near the US/Mexico border line in Altar town, Nogales, northwestern MexicoGuillermo Arias/AFP
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16 February 2017: Hand prints are seen on the US/Mexico border fence in Nogales, northwestern MexicoGuillermo Arias/AFP
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16 February 2017: A boy rides a bicycle next to a mural honouring migrants who dies crossing the desert, in Altar, northwestern MexicoGuillermo Arias/AFP
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16 February 2017: A portrait of Jose Antonio Elena Rodriguez, a 16-year-old minor shot by a Border Patrol agent who – according to a CBP investigation – acted in self deffence, is seen on the US/Mexico border fence in Nogales, northwestern MexicoGuillermo Arias/AFP
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16 February 2017: The US-Mexico border fence runs through NogalesGuillermo Arias/AFP