Last Wednesday, The Washington Post ran an article about The History of U.S. Border Wall Apprehensions. There were several interesting data visualizations in the article, but the one that really caught my eye was their heatmap (or density map) showing apprehensions at the U.S.-Mexico border, which is along the southern portion of the United States (see screenshot below).
In Tableau, heatmaps or density maps can be created to reveal the patterns or relative concentrations that might otherwise be hidden due to an overlapping mark on a map. Tableau creates a heatmap by grouping overlaying marks and color-coding them based on the number of marks in the group.
In The Washington Post heatmap, the fence type is represented by a red line if it is for pedestrians and a black line if it is for vehicles. The density color (grouping of marks) for border patrol apprehensions in the fiscal year 2017, becomes more Orange in color and deeper shades of Orange for the more apprehensions that occurred (see two screenshots below). NOTE: Sources used for this article are listed at the end of this blog post.
As you can see in the screenshot below, for my home State of Arizona, Nogales is an area of high activity for border patrol apprehensions.
I thought this heatmap excellently showed you quickly what type of fence was present at a particular point along the border, as well as the number of apprehensions at any particular point.
Some Background on U.S.-Mexico Border Patrol Apprehensions
According to numbers released by the Department of Homeland Security, nationwide apprehensions of migrants entering the country without authorization are at some of their lowest numbers in decades. The U.S. Border Patrol states on its website that these numbers do not include individuals met at ports of entry looking to enter legally, but are determined to be inadmissible, or individuals seeking humanitarian protection under U.S. law. 
In 2018, U.S. Border Patrol took int custody just over 400,000 people illegally entering the United States, down from the second-high of 1.67 million in 2000. 
The Washington Post Fact Checker Salvador Rizzo reported that most of these declines have come, “partly because of technology upgrades; tougher penalties in the wake of the 9/11 terrorist attacks; a decline in migration rates from Mexico; and a sharp increase in the number of Border Patrol officers.” 
The first iteration of current fencing along the U.S.-Mexico took place during the 1990s where the administrations of Presidents George H.W. Bush and Bill Clinton authorized the construction of fencing along the California-Mexico border. Then, in 2006, President George W. Bush expanded the border fence by signing the Secure Fence Act into law, which authorized the construction of a fence along 700 miles of the U.S.-Mexico border. 
Apprehensions of unaccompanied minors at the border from El Salvador, Honduras and Mexico began to decline in 2016 and 2017 from previous highs in 2014, according to Border Patrol statistics. Guatemala, however, has seen a large increase in apprehensions of minors at the border, reaching a high of just over 22,000 in 2018, the largest of any country within the past five years. 
The rise of violence in some Central American countries has caused migrants and asylum seekers to head to the United States. According to a U.N. High Commissioner for Refugees report from 2015, “increasing violence in Guatemala, El Salvador and Honduras has led to a fivefold increase in pending asylum cases — now 109,800 — in Mexico and the United States since 2012.” 
Detainments along the U.S.-Mexico border saw an overall decline of 81.5 percent from 2000 to 2017. The border fence near the Rio Grande Valley is the only border crossing that has seen an increase in apprehensions within that same time frame (see screenshot below). 
 Brittany Renee Mayes, Aaron Williams and Laris Karklis, The history of U.S. border apprehensions, The Washington Post, January 9, 2019, Updated: January 10, 2019, https://www.washingtonpost.com/graphics/2019/national/trump-border-wall-arrests/?utm_term=.11ba1329299d.
 PHOTO: Berlinger, Joshua, Mexican lawmaker climbs border wall in stunt aimed at Trump, CNN, March 3, 2017, https://www.cnn.com/2017/03/03/americas/mexican-lawmaker-border-wall-trnd/index.html.
 PHOTO: WKRG, Immigrants climb over U.S. Mexico border wall, YouTube, FOX 10 Phoenix, September 6, 2016, https://www.youtube.com/watch?v=1dkLJcQrvLY.