This graphic, from a San Diego Union-Tribune article that appeared Saturday, includes data that we almost never get to see: real-time information on U.S. border authorities’ drug seizures. (Click on it, or here, to view it larger.)

The data covers just one sector of the U.S.-Mexico border, which Border Patrol divides into nine sectors. This is the San Diego sector, which covers the western half of California’s border with Mexico. 2015 and 2016 data shows this to be the number-one sector, by far, for seizures of heroin and methamphetamine, both of which generally get produced in Mexico’s Pacific coast region. San Diego is also number two for cocaine seizures.

Seizure data gives you at least a vague idea of how much drugs are being trafficked through a sector. In 2015, the DEA reported [PDF], 49% of all heroin and 57% of all methamphetamine that got seized anywhere at the border was seized in the San Diego sector.

San Diego is also one of the most walled-off sectors, with fence built over 46 of its 60 border miles. So it’s a good test case for what a lot of border wall-building might achieve.

The chart here is even more useful because it breaks the seizure information down between what is seized at official border crossings, or “ports of entry” (bottom row), and what is seized in between the ports of entry, where Border Patrol operates and where walls get built (top row).

Look closely at the vertical (y-axis) scale on these charts. The maximum number at the top of each is several times higher for ports of entry than it is for “Border Patrol.” This means that several times more drugs get found at the ports—in cargo containers, hidden in vehicles, carried by people—than in the “in-between” areas where one might build a border wall.

Simply dividing the top-line of the “ports of entry” graphs by the top-line of the “Border Patrol” graphs—a horribly imperfect measure—gives you this general ratio of seizures.

  • Marijuana: 5 times more seizures at ports than between ports (400,000 pounds ÷ 80,000 pounds).
  • Methamphetamine: 17 times more seizures at ports than between ports.
  • Cocaine: 8 times more seizures at ports than between ports.
  • Heroin: 2.5 times more seizures at ports than between ports (though it’s a rough 1:1 ratio in 2016 and 2017).

The unavoidable conclusion here: building more border wall will have minimal effect on the transit of illegal drugs from Mexico into the United States. If you want to make it harder to transship drugs northward, you have to focus on the ports of entry, which have $5 billion in unmet infrastructure needs and are short-staffed by about 2,000 officers.

The ports are less “sexy” than a big concrete wall, but making them function better would do far more to disrupt drug flows. But the Trump administration’s funding requests have so far included no increases for ports of entry.

Postscript: Note that these charts’ 2017 column represents only the first six months of the government’s Fiscal Year 2017 (which started on October 1 of last year), which is why it looks like seizures went down during the most recent year. Double the size of that column, and you get a rough idea of what end-of-year 2017 seizures might look like. At the current pace, San Diego would see sharply more 2017 seizures of cocaine and methamphetamine, a small increase in heroin, and a sharp drop in cannabis.