How many continents are there?

Come on kids, between us we can crack this. Image: Getty.

Once upon a time, “How many continents are there” was one of those questions with straightforward answers, like “How many colours are in a rainbow” or “what is the weather like in summer”. There are seven. Of course there are seven: all those picture books I had as a kid said there were seven.

Except, it turns out that, as with so many of the things we tell our children, this number owed as much to social convention as it does to objective reality. And social conventions can differ: depending on where you are in the world, there can be anywhere between four and seven continents, and you sometimes don’t have to travel very far to get a different answer.

So, to coin a phrase: what on Earth is going on?

Rules and regulations

First define your continent. The Wikipedia page on the matter contains this helpful explanation:

By convention, “continents are understood to be large, continuous, discrete masses of land, ideally separated by expanses of water”.

Which sounds simple enough. Except the very next sentence is this:

Many of the seven most commonly recognized continents identified by convention are not discrete landmasses separated completely by water.

Which feels like an unexpected piece of dry humour from an open-sourced encyclopaedia.

But it has a point: it’s the work of all of four seconds to think of vast numbers of ways in which the seven things you almost certainly think of as continents don’t fit this rule. Off the top of my head:

  • Islands like Great Britain are considered part of continents despite not being part of continuous masses of land;

  • North and South America are not discrete masses of land, they’re connected by an isthmus;

  • Neither are Africa and Asia;

  • Europe and Asia aren’t even vaguely separated, they’re quite obviously the same bloody thing;

  • If Europe gets to be a continent because it’s separated from Asia by some mountains and some inland seas, then why is India only a sub-continent?

  • If Australia is a continent why is Greenland only an island? Okay, it’s smaller, but where’s the line? What are the rules here?

And so on and so on.

Spinning plates

There is another way of dividing the Earth up into roughly continent sized bits, which has a rather more scientific basis to it: plate tectonics, the geological theory which explains mountain ranges, volcanoes, and so on by showing how bits of the Earth’s surface have been sliding about and banging into each other for the last few billion years.

In this theory, it’s quite obvious why the Americas are two continents, why Australia is one but Greenland isn’t, and why Africa is a different thing to Asia despite being attached to it. It also highlights a very good reason for considering Britain to be part of Europe: they’re part of the same continental shelf, even if part of that shelf is submerged under water. Despite Brexit, Britain will always be in Europe.

The plates. Click to expand. Image: USGS/Wikimedia Commons.

In many other ways, though, the map of the tectonic plates doesn’t look anything like the map of the continents. For one thing there are a bunch of oceanic ones, which on maps of the world are mostly just water with a few islands in them.

For another, the Middle East and India are their own plates, so aren’t part of Asia; neither is the Russian Far East, which is actually part of the North American plate. Europe, meanwhile, very clearly is part of Asia, except for Iceland, which is half Asian, half North American.

There are good reasons why plate tectonics isn’t going to get us very far in explaining why we mostly think we have seven continents. One is that it’s a surprisingly recent theory: it wasn’t widely recognised by the scientific community until the 1960s, so there are plenty of people around now whose school text books will have laughed at the idea.

Another is that the plate boundaries are often invisible or, at least at the human scale, nonsensical: any system which splits Iceland into two separate continents is not going to be a useful categorisation.

Geography is written by the victors

The real reason we count Europe as a continent and include Britain in it, treat India as a part of Asia, and so forth is (this is where we came in) social convention: we do it because we do.

More than that, we do it because the rules on this stuff were largely formulated by the Europeans who spent much of the last five hundred years or so conquering the world. That’s why Europe is a seen as a single, diverse continent but the Indian subcontinent, with its own patchwork of languages, cultures and religions, isn’t: because the former was the imperial power that conquered the latter.

A related point is that, if you ignore plate tectonics, the entire world doesn’t divide neatly up into continents at all. The reason a huge bunch of Pacific islands get bundled together with Australia as a slightly miscellaneous category called “Oceania” is as much because people wanted to make everything fit in somewhere, as it is because of any real connection between the two.

So those lengthy explanations aside, how many continents actually are there?

Counting continents

There seem to be six different systems, helpfully portrayed in this gif:

A gif of the various models. Click to expand. Image: AlexCovarrubia/Wikimedia Commons.

The seven continent system is the one you’re probably familiar with. That’s the one that’s standard in the English-speaking world, China, south Asia, and parts of western Europe. The British Empire can probably be blamed, at least in part, for its dominance.

There’s also an ultra-stripped down four continent model which divides the world into four major landmasses: Eurasia-Africa, America, Antarctica, Australia. This, best I can tell, isn’t taught anywhere; but it is the logical end point of the definition that involves big bits of land divided by water, so it’s worth including it anyway.

In between there are four other models:

  • A six-continent system in which Europe and Asia are one continent. This, the internet tells me, is the standard in Russia and Eastern Europe (which makes sense, given that the slavic world straddles the Urals), and also Japan (although, citation needed).

  • A different six-continent system treats Europe and Asia as separate, but combines North and South America. That one seems to be favoured in France, much of southern Europe and various places colonised by those countries.

  • There’s also a five continent system which combines the Americas but ignores Antarctica because, to the first approximation, nobody lives there. This is the one favoured by the UN and the International Olympic Committee (count the rings).

  • Lastly, there’s a variant five-continent system consisting of Eurasia, America, Africa, Australia and Antarctica. I can find no reference whatsoever to anyone using this one, but it’s in the gif and also this National Geographic page, so I’m including it for the sake of completism.

So, there you go. The best we can say is that the world has “some continents”. Assuming you accept the notion that continents exist at all.

I’m still really angry at those picture books which promised me snow in winter and heat in summer, incidentally.

Jonn Elledge is the editor of CityMetric. He is on Twitter as @jonnelledge and also has a Facebook page now for some reason.

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To build its emerging “megaregions”, the USA should turn to trains

Under construction: high speed rail in California. Image: Getty.

An extract from “Designing the Megaregion: Meeting Urban Challenges at a New Scale”, out now from Island Press.

A regional transportation system does not become balanced until all its parts are operating effectively. Highways, arterial streets, and local streets are essential, and every megaregion has them, although there is often a big backlog of needed repairs, especially for bridges. Airports for long-distance travel are also recognized as essential, and there are major airports in all the evolving megaregions. Both highways and airports are overloaded at peak periods in the megaregions because of gaps in the rest of the transportation system. Predictions for 2040, when the megaregions will be far more developed than they are today, show that there will be much worse traffic congestion and more airport delays.

What is needed to create a better balance? Passenger rail service that is fast enough to be competitive with driving and with some short airplane trips, commuter rail to major employment centers to take some travelers off highways, and improved local transit systems, especially those that make use of exclusive transit rights-of-way, again to reduce the number of cars on highways and arterial roads. Bicycle paths, sidewalks, and pedestrian paths are also important for reducing car trips in neighborhoods and business centers.

Implementing “fast enough” passenger rail

Long-distance Amtrak trains and commuter rail on conventional, unelectrified tracks are powered by diesel locomotives that can attain a maximum permitted speed of 79 miles per hour, which works out to average operating speeds of 30 to 50 miles per hour. At these speeds, trains are not competitive with driving or even short airline flights.

Trains that can attain 110 miles per hour and can operate at average speeds of 70 miles per hour are fast enough to help balance transportation in megaregions. A trip that takes two to three hours by rail can be competitive with a one-hour flight because of the need to allow an hour and a half or more to get to the boarding area through security, plus the time needed to pick up checked baggage. A two-to-three-hour train trip can be competitive with driving when the distance between destinations is more than two hundred miles – particularly for business travelers who want to sit and work on the train. Of course, the trains also have to be frequent enough, and the traveler’s destination needs to be easily reachable from a train station.

An important factor in reaching higher railway speeds is the recent federal law requiring all trains to have a positive train control safety system, where automated devices manage train separation to avoid collisions, as well as to prevent excessive speeds and deal with track repairs and other temporary situations. What are called high-speed trains in the United States, averaging 70 miles per hour, need gate controls at grade crossings, upgraded tracks, and trains with tilt technology – as on the Acela trains – to permit faster speeds around curves. The Virgin Trains in Florida have diesel-electric locomotives with an electrical generator on board that drives the train but is powered by a diesel engine. 

The faster the train needs to operate, the larger, and heavier, these diesel-electric locomotives have to be, setting an effective speed limit on this technology. The faster speeds possible on the portion of Amtrak’s Acela service north of New Haven, Connecticut, came after the entire line was electrified, as engines that get their power from lines along the track can be smaller and much lighter, and thus go faster. Catenary or third-rail electric trains, like Amtrak’s Acela, can attain speeds of 150 miles per hour, but only a few portions of the tracks now permit this, and average operating speeds are much lower.

Possible alternatives to fast enough trains

True electric high-speed rail can attain maximum operating speeds of 150 to 220 miles per hour, with average operating speeds from 120 to 200 miles per hour. These trains need their own grade-separated track structure, which means new alignments, which are expensive to build. In some places the property-acquisition problem may make a new alignment impossible, unless tunnels are used. True high speeds may be attained by the proposed Texas Central train from Dallas to Houston, and on some portions of the California High-Speed Rail line, should it ever be completed. All of the California line is to be electrified, but some sections will be conventional tracks so that average operating speeds will be lower.

Maglev technology is sometimes mentioned as the ultimate solution to attaining high-speed rail travel. A maglev train travels just above a guideway using magnetic levitation and is propelled by electromagnetic energy. There is an operating maglev train connecting the center of Shanghai to its Pudong International Airport. It can reach a top speed of 267 miles per hour, although its average speed is much lower, as the distance is short and most of the trip is spent getting up to speed or decelerating. The Chinese government has not, so far, used this technology in any other application while building a national system of long-distance, high-speed electric trains. However, there has been a recent announcement of a proposed Chinese maglev train that can attain speeds of 375 miles per hour.

The Hyperloop is a proposed technology that would, in theory, permit passenger trains to travel through large tubes from which all air has been evacuated, and would be even faster than today’s highest-speed trains. Elon Musk has formed a company to develop this virtually frictionless mode of travel, which would have speeds to make it competitive with medium- and even long-distance airplane travel. However, the Hyperloop technology is not yet ready to be applied to real travel situations, and the infrastructure to support it, whether an elevated system or a tunnel, will have all the problems of building conventional high-speed rail on separate guideways, and will also be even more expensive, as a tube has to be constructed as well as the train.

Megaregions need fast enough trains now

Even if new technology someday creates long-distance passenger trains with travel times competitive with airplanes, passenger traffic will still benefit from upgrading rail service to fast-enough trains for many of the trips within a megaregion, now and in the future. States already have the responsibility of financing passenger trains in megaregion rail corridors. Section 209 of the federal Passenger Rail Investment and Improvement Act of 2008 requires states to pay 85 percent of operating costs for all Amtrak routes of less than 750 miles (the legislation exempts the Northeast Corridor) as well as capital maintenance costs of the Amtrak equipment they use, plus support costs for such programs as safety and marketing. 

California’s Caltrans and Capitol Corridor Joint Powers Authority, Connecticut, Indiana, Illinois, Maine’s Northern New England Passenger Rail Authority, Massachusetts, Michigan, Missouri, New York, North Carolina, Oklahoma, Oregon, Pennsylvania, Texas, Vermont, Virginia, Washington, and Wisconsin all have agreements with Amtrak to operate their state corridor services. Amtrak has agreements with the freight railroads that own the tracks, and by law, its operations have priority over freight trains.

At present it appears that upgrading these corridor services to fast-enough trains will also be primarily the responsibility of the states, although they may be able to receive federal grants and loans. The track improvements being financed by the State of Michigan are an example of the way a state can take control over rail service. These tracks will eventually be part of 110-mile-per-hour service between Chicago and Detroit, with commitments from not just Michigan but also Illinois and Indiana. Fast-enough service between Chicago and Detroit could become a major organizer in an evolving megaregion, with stops at key cities along the way, including Kalamazoo, Battle Creek, and Ann Arbor. 

Cooperation among states for faster train service requires formal agreements, in this case, the Midwest Interstate Passenger Rail Compact. The participants are Illinois, Indiana, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, and Wisconsin. There is also an advocacy organization to support the objectives of the compact, the Midwest Interstate Passenger Rail Commission.

States could, in future, reach operating agreements with a private company such as Virgin Trains USA, but the private company would have to negotiate its own agreement with the freight railroads, and also negotiate its own dispatching priorities. Virgin Trains says in its prospectus that it can finance track improvements itself. If the Virgin Trains service in Florida proves to be profitable, it could lead to other private investments in fast-enough trains.

Jonathan Barnett is an emeritus Professor of Practice in City and Regional Planning, and former director of the Urban Design Program, at the University of Pennsylvania. 

This is an extract from “Designing the Megaregion: Meeting Urban Challenges at a New Scale”, published now by Island Press. You can find out more here.