Mayor Bob Filner has vowed to take better advantage of San Diego’s neighbor to the south.

He’s pledged to improve relations with Tijuana officials, open an office in the Baja California city and work to lessen wait times at the border.

As he’s talked about those goals, Filner and others have emphasized that the two cities make up one of the world’s biggest mega regions.

He made a similar statement in a December press release: “We live in the world’s largest metropolitan binational region and we need to work with Mexico on improving our regional competitiveness in order to attract new investments, more tourism and create new jobs.”

Urban planners say a binational region consists of cities in two different countries whose government and business operations are somehow integrated. That can mean the communities collaborate on regional planning and transportation networks, public health or other initiatives or that their economies are linked in some way.

We talked to several professors and regional experts who have spent years studying border communities. None could say whether San Diego/ Tijuana makes up the largest metropolitan binational region in the world, only that it’s likely among the world’s largest.

So just how big is it?

Paul Ganster, director of San Diego State University’s Institute for Regional Studies of the Californias, said most population estimates incorporate residents outside San Diego and Tijuana boundaries.

They include San Diego County and Tijuana, which have a combined population of at least 4.7 million, according to census data. Adding Tecate and Playas de Rosarito, two smaller communities near Tijuana, to the count boosts the number to about 4.9 million residents.

A regional group that aims to draw new businesses to the region has an even broader definition.

The Cali Baja Bi-National Mega-Region includes San Diego and Imperial counties, as well as the entire state of Baja California in its count. That would put the region’s population closer to 6.5 million, according to the latest census figures.

The enormous amount of travel between the two cities suggests some level of integration.

San Ysidro, one of three border crossings in the region, has consistently been ranked among the busiest along the U.S.-Mexico border.

More than 30 million pedestrians and passengers crossed the border in 2011, according to U.S. Department of Transportation data.

The cities of San Diego and Tijuana have binational affairs offices to coordinate relations between the two cities. Mayors from both cities have worked together to lobby their federal counterparts for additional resources and infrastructure at border crossings. Various business groups, including the San Diego Regional Chamber of Commerce, have developed regional partnerships with Mexican officials. SANDAG, the county’s regional planning agency, also has a committee that addresses cross-border issues. We’ll explore this cooperation further in an upcoming story.

But not everyone is convinced that San Diego is truly a binational region.

Oscar Romo, a lecturer in the University of Southern California-San Diego’s urban studies and planning department, said the two cities must better coordinate in key areas such as water treatment and infrastructure.

“The leaders have completely different sets of priorities,” he said. “While the integration could be great, while the economic power of the two cities could jointly do a lot, it’s not happening.”

How does its size compare to other binational regions?

Some of the other largest metropolitan binational regions that are dominated by or composed of two major cities:

El Paso, Texas/Ciudad Juárez, Chihuahua, Mexico: This area is often cited in lists of the world’s largest binational metro areas but the San Diego/Tijuana region is larger. Census estimates from the U.S. and Mexico suggest the two cities have about 2.1 million residents. The two consider each other “sister cities” and many residents have family members or jobs across the border.

Romo said this area is a true binational region because the two cities built up together and have a long tradition of cooperation.

He acknowledged the region also benefits from something San Diego and Tijuana have less control over: shorter border crossing waits.

Shorter lines make it easier for residents on both sides of the border to cross for a quick shopping trip or business meeting, something that San Diego and Tijuana residents can’t do unless they have a special pass that allows them to bypass the longest lines.

A 2007 SANDAG report estimated the binational region lost $7.2 billion in potential output and more than 62,000 jobs due to logjams at the border.

Detroit/Windsor, Ontario, Canada: Wayne County, Mich., which is dominated by Detroit, has about 1.8 million residents while a Canadian population count put Windsor at about 210,900 residents. The region was once larger but Detroit’s population has fallen in recent years. Today, the region has about 2 million residents. Some population counts also include other cities and counties in Michigan, Canada and Ohio. Leaders in the region, which centers on the Detroit River, have collaborated on transportation corridors and been tied by the auto industry for decades.

Vienna, Austria/Bratislava, Slovakia: Population counts from these countries show about 2.1 million people live in this region, which is made up of Austria and Slovakia’s capital cities. The majority, about 1.7 million, live in Vienna. Cooperation between the two cities was long stalled until after the decline of communist influences in 1989. In 2010, city leaders signed an agreement to partner on planning, trade and other efforts.

Kinshasa, Democratic Republic of the Congo/Brazzaville, Republic of the Congo: This east African region turned out to be the largest binational territory we came across. In 2010, the United Nations estimated that about 8.8 million people lived in Kinshasa and another 1.3 million lived in Brazzaville. Like San Diego and Tijuana, a border complicates the two cities’ relations but this region deals with a different kind of border headache: the Congo River. Crossers must ride ferries to get across the border. A 2011 study commissioned by World Bank, which provides assistance to developing countries, noted the relative lack of trade due to the need for improved transport between the two cities. A survey included in the report revealed a single trip across the border could cost as much as $48 U.S. dollars .

A bridge could boost relations between the two cities. A Republic of Congo official announced in 2011 that his country had secured funding for a related study.

Kinshasa, the larger of the two cities, is no stranger to the world stage. In 1974, the city hosted the “Rumble in the Jungle” between legendary boxers Muhammad Ali and George Foreman.

But the majority of its nearly 4,000-mile area remains rural despite a crowded urban core. That could change. The United Nations predicts the region could grow to 14.5 million residents by 2025.

Do you know of any other binational regions worth mentioning? How do San Diego and Tijuana’s efforts to work together as a region compare to cross-border efforts across the world? We’d love to hear from you.

Lisa Halverstadt is a reporter at Voice of San Diego. Know of something she should check out? You can contact her directly at or 619.325.0528.

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Disclosure: Voice of San Diego members and supporters may be mentioned or have a stake in the stories we cover. For a complete list of our contributors, click here.

Lisa is a senior investigative reporter who digs into some of San Diego's biggest challenges including homelessness, city real estate debacles, the region's...

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