America’s Wall: How we crunched the numbers

By Brandon Quester and Leonardo Castañeda | inewsource

November 13, 2017

America’s Wall is the culmination of months of reporting and data analysis to better understand the evolution of the U.S.-Mexico border wall and its impact on illegal immigration.

Other news organizations have reported extensively on the length — and gaps — of the border wall, including many efforts to map where today’s fencing exists.

KPBS and inewsource were interested in the specific fencing types and locations so we could build a precise map of the modern wall. To do that we filed a Freedom of Information Act request to U.S. Customs and Border Protection asking for detailed mapping data showing the location and makeup of every piece of the wall.

In response to our request, CBP provided two digital map files detailing more than 3,600 individual sections of the border wall. These records formed the foundation of our reporting.

As with every major data project, for complete transparency and disclosure, we’re sharing our process and data methodology.


For each section of wall, the files included information such as type of fencing, year construction was completed, and the state and Border Patrol sector in which it was built. The oldest section of wall in these records dates from 1962. The newest section is from May 2015.

CBP grouped fencing under two umbrella types based on what the barrier was intended to stop: pedestrians or vehicles. Those umbrella types were broken down further into more specific subtypes: Pedestrian fencing consisted of primary, secondary and tertiary sections; vehicle fencing was divided into permanent and temporary structures. You can read those definitions here:

Border Fencing

Two main types of fencing comprise the U.S. wall with Mexico: pedestrian and vehicle. Those are then divided into more categories:

It can vary widely but was built with intention of stopping foot traffic. This fencing is divided into three types: primary, secondary and tertiary.

  •  Primary pedestrian: It covers 403 miles and makes up the bulk of fencing along the border. It ranges from corrugated steel landing mats to taller steel wall structures.
  • Secondary pedestrian: It covers 42 miles in four urban areas. Often it’s marked by tall steel walls with barbed wire at the top. Border Patrol places security, flood lights and roads between it and primary fencing.
  • Tertiary pedestrian: It covers less than 17 miles in three locations. In San Diego, it’s often barbed wire fencing.

It is intended to stop car traffic and is often little more than metal poles. This fencing is divided into two types: permanent and temporary.

  • Permanent vehicle: Most of the 181 miles of this fencing is in Arizona. It can be as simple as railroad ties forming a rudimentary picket fence.
  • Temporary vehicle: Most of the almost 119 miles of this fencing is in El Centro; Tucson, Arizona; and El Paso, Texas. Some it is called “Normandy” fencing — metal X’s holding railroad ties.

Each piece of fencing included a “date_in” attribute, which details when construction of that piece of fencing was completed. But in our vetting process of the data, we came across sections that either did not have a specific year attached or which had an estimate for the year of completion.

These undated sections account for 0.18 miles of total fencing, or 0.02 percent of the total wall. We included them in the total fencing calculations used throughout this project and referenced in our map, but the actual polygons, or shapes detailing pieces of fencing, were not plotted on our interactive map.

We handled on a case-by-case basis the fencing that had an estimate for when it was completed. For example, sections of fencing built in the 1970s were grouped in a broad estimate, which we counted as 1970, the earliest possible date. Fencing built in the 1980s gives a specific year, but lists it as an estimate. In those cases, we used the years estimated. Other sections gave a specific year but estimated the month of completion, or indicated a fiscal year but not a calendar date. We limited our analysis to years.

The files CBP provided give an extraordinarily detailed look at fencing that makes up the U.S-Mexico border. However, some elements were not included. Most notably, the digital map provided the length of each section of fencing in an “internal unit” — something other than feet or meters — which we were unable to convert into usable measurements.

Instead, using open source digital mapping software, we were able to extract the length in feet for each section of wall. Although the process is technically difficult — adjusting for the curvature of the Earth on a 2D projection requires some fancy math — the program was able to easily produce an incredibly detailed understanding of the wall.

The shortest section of the wall measured just 2 feet, 5 inches, in Del Rio, Texas. The longest single section, in Yuma, Arizona, spanned almost 15 miles.

Another gap in the data provided is that the map only shows the fencing as it exists today. It doesn’t show what, if anything, existed along the border before the now-standing wall was built.

Additional data

In addition to the detailed map data, we layered decades of other CBP statistics to add context.

Apprehension data on the map shows how many people were detained annually from 1960 through 2016 for attempting to enter the U.S. illegally. Apprehensions do not include deportations handled by U.S. Immigration and Customs Enforcement. They also do not include migrants who tried to enter the U.S. at a port of entry but were declared inadmissible.

The apprehension data CBP provided was broken down by the nine Border Patrol sectors along the Southwest border: two in California (San Diego and El Centro); two in Arizona (Yuma and Tucson); four in Texas (Big Bend, Del Rio, Laredo and Rio Grande Valley); and one that covers all of New Mexico and part of Texas (El Paso).

For our analysis of which Border Patrol sector had the greatest share of apprehensions, we used two primary calculations:

  • The first is the total number of apprehensions along the U.S.-Mexico border, by year. This information is defined in the document as “Southwest Border Total.”
  • The second analysis shows each sector’s share of total apprehensions, by year. This calculation was done by dividing apprehensions, by sector and year, with total apprehensions along the border for that year.

Because the building of the wall often was accompanied by an increase in Border Patrol staffing, we also showed on the map the number of agents for each year from 1992 through 2016.

If you have questions or comments about the map, the data or our America’s Wall project, email us at [email protected].