The Øresund Bridge (Øresundsbroen), stretching across the Øresund between Denmark and Sweden, is a number of things.

Firstly, it’s oppressive, because everybody forgets about the Drogden Tunnel that makes up half the crossing. Poor Drogden. Secondly, it’s incredibly popular, with about 20,000 vehicles using it every single day – even while the ferry that does the same journey is still one of the busiest international ferry routes in the world. And thirdly, yes, it is that Bridge from hit Scandi Noir drama The Bridge.

That link – between Malmö in Sweden and Copenhagen in Denmark – is clearly crucial. You don’t just go making TV series about any old bridge: you make it about something that has a symbolic significance, that provides a vital link, that helps two cities in different countries to  work as one.

Copenhagen – Malmö

The Bridge (the TV show, not the actual bridge) is in itself a pretty good way of thinking about the relationship between Copenhagen – the Danish capital – and the Swedish city of Malmö. It’s a joint production between Sveriges Television from Sweden and Danmarks Radio of Denmark, starring Swedish actress Sofia Helin as a Swedish detective and Danish actor Kim Bodnia as a Danish detective. They team up to solve cross-border mysteries in a picture-perfect (if you ignore all the murders) tale of international cooperation.

What The Bridge doesn’t tell you about is that Copenhagen and Malmö have ties stretching back centuries. Scania, the bit of Sweden of which Malmö is the largest city, was in Danish hands for much of the Middle Ages, and the Øresund was hotly contested in various skirmishes between Denmark and Sweden throughout the Renaissance.

These days, the scent of Dano-Swedish war is far off, and the region has its own governmental cooperation structure, the Øresund Committee; it’s benefitted from EU funding to enhance cross-border activity at regular intervals, too. The Copenhagen Port and Malmö Harbour work together in the joint CMP (Copenhagen Malmo Port) authority, sharing the spoils and toils of being a major gateway to the Baltic sea region. A consortium of twelve universities was founded in 1997 to foster academic cooperation, too.

That being said, the relationship between the two isn’t without its flaws. The job market in Copenhagen is in much ruder health than that of Malmö, whilst the housing market in the area around Malmö isn’t so hot. Essentially, this means a lot of locals live in Sweden and commute over to Denmark for work.

This causes all sorts of problems. Municipal budgets get squeezed because people contribute to the economy of city in which they work rather than the one in which they live. Some people find themselves paying taxes in both countries – or neither. And voting is a tricky business, if you spend all your time in one country, but because you wanted a nice house you’re only allowed to vote in the other one, which has your bed in it.

All that being said, when your wages are high as a kite relative to the rest of the world, and your main problems are that one city has so many great jobs whilst the other has reasonably affordable housing, it’s hard not to have Justin Timberlake’s 2002 Grammy Award-winning hit Cry Me A River pounding through your head like a heavy-duty SUV trundling over the Øresundsbroen.

Fear not. Idyllic Scandi cross-waterway metropolises aren’t the only examples of cities either side of an international borderline making a solid double act.

San Diego – Tijuana

To the left is Mexico, to the right the US; the receding yellow lines mark the border fence.

The San Ysidro Point of Entry is the busiest land border crossing in the world. In 2005 alone, almost 41.5m people crossed the border between the Mexican state of Baja California and southern California in the United States.

San Diego, on the northern side, is the second-largest city in California. It’s home to the largest naval fleet in the world, coastal canyons to die for, and the world’s most enigmatically named neighbourhood, “Normal Heights”. Meanwhile on the Mexican side, Tijuana is a manufacturing heavyweight, tourism hotspot, and cultural boomtown.

The North American Free Trade Agreement is a trade bloc that came into force in 1994, and is the cornerstone of the cross-border symbiosis between the two cities. Though labour costs are vastly cheaper in Mexico, the workforce – attracted by the proximity to the US – is still skilled and diverse, making Tijuana an attractive place to make things. A large chunk of those things can then be hauled over to San Diego and sold onwards.

Americans, meanwhile, make a habit of hopping over to Mexico to take advantage of its more liberal offerings. With a drinking age of only 18, a culture of Latin music and plentiful dancing, and a legal and regulated prostitution industry, Tijuana is to San Diego what a night out with the lads is to a cup of tea with your Granny. Each has its own merits, but only with both can a fully rounded life be lived.

London – Westminster

It’s easy to forget it, but the world’s best example of two cities working together symbiotically is right here in London. The City of London and the City of Westminster have splurged into each other over the course of the centuries, but still retain their very particular identities, rooted in their own histories and with their own sense of purpose.

The City of London is a political oddity, being a corporation, and is probably the world’s oldest continuously-elected local government authority. It is the older of the two cities, which explains in part the fact that it was the destination of the world’s first underground rail line, and has maintained its original role as a vital trading place in its contemporary association with finance, banking, and business.

Westminster, meanwhile, has its foundations in the Church and the Crown. As its name suggests, it is the church in the west, as opposed to St. Paul’s in London. Westminster Abbey is a royal peculiar – a church directly under the jurisdiction of the Queen – and is at the centre of a tapestry of royal history that takes in a dense concentration of royal palaces. Many no longer have such royal associations, but Whitehall Palace, Westminster Palace, St. James’s Palace, Banqueting House, Clarence House, Buckingham Palace, Lancaster House, and the Royal Mews are all royal foundations rooted in the royal city of Westminster.

An increase in settlement in the space between the two, such as along the Strand – which used to be, as the name suggests, a beach – has blurred the boundaries between the two cities. So, too, has the intensive bombing of London in World War Two, which led to many businesses relocating or starting up in Westminster or elsewhere in the area as the City of London was rebuilt.

To this day, the two cities work with and against each other to make London the fearsome powerhouse it is today. It takes more than one city to become the Death Star sucking all the life out of the rest of the country, you know.

Fort Worth – Dallas

Oh look, an airport.

They may not have as much history as London and Westminster, or cross international boundaries like Copenhagen and Malmo, but Dallas and Fort Worth in Texas are profoundly different cities, helping each other along as they go.

Culturally, the two are miles apart (about 30, to be exact). The Lonely Planet travel guide puts it rather nicely: “Dallas and Fort Worth may be next-door neighbors, but they’re hardly twins – or even kissing cousins. Long regarded as being divergent as a Beemer-driving sophisticate and a rancher in a Ford pickup truck, these two cities have starkly different facades.”

A friend who lives nearby explained it to me in gay bar terms: “Dallas is the bar filled with slick city-boys in suits with martinis, while Fort Worth is the guilty pleasure bar jammed with wholesome boys in lumberjack shirts like the ones you pretend not to love from Brokeback Mountain.”

Which makes some kind of sense. Dallas is dominated by business and technology. It’s one of the most densely packed areas of the US in terms of high-tech industry, with the area becoming known as the “Silicon Prairie” or “Telecom Corridor”, depending on which tacky moniker you hate least.  Fort Worth, by contrast, is the capital of the farming and ranching industries of Texas – which are, of course, very important. Because it’s Texas.

Similarly, being Texas means there’s a lot of Republicans around, but the area’s politics can tell you something about the two cities. There’s one congressional district that covers the central parts of both cities (in classic US Congress gerrymandering fashion), and which is held by a Democrat. Other than that, every congressional district covering the greater metropolitan area is held by a Republican – except for one. The 30th, which covers southern Dallas. Go figure.

Cities are heavyweight money-makers, life-changers, and culture-developers. But when they work together – across national borders, straits of water, or cultural differences – they become even more formidable.

Images: Getty.