Today, megacities have become synonymous with economic growth. In both developing and developed countries, cities with populations of 10 million or more account for one-third to one-half of their gross domestic product.

Many analysts and policymakers think this trend is here to stay. The rise of big data analytics and mobile technology should spur development, they assert, transforming metropolises like Shanghai, Nairobi and Mexico City into so-called "smart cities" that can leverage their huge populations to power their economies and change the power balance in the world.

As technology researchers, however, we see a less rosy urban future. That's because digitisation and crowdsourcing will actually undermine the very foundations of the megacity economy, which is typically built on some combination of manufacturing, commerce, retail and professional services.

The exact formula differs from region to region, but all megacities are designed to maximise the productivity of their massive populations. Today, these cities lean heavily on economies of scale, by which increased production brings cost advantages, and on the savings and benefits of co-locating people and firms in neighbourhoods and industrial clusters.

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But technological advances are now upending these old business models, threatening future of megacities as we know them.

Manufacturing on the fritz

One classic example of a disruptive new technology is 3-D printing, which enables individuals to "print" everything from ice cream to machine parts.

As this streamlined technique spreads, it will eliminate some of the many links in the global production process. By taking out the "middle men," 3-D printing may ultimately reduce the supply chain to just a designer on one end and a manufacturer on the other, significantly reducing the production costs of manufactured goods.