Provide services and protection? Just to start.
Just one policeman per 1,000 citizens would mean a 420,000 person police force.
China to create largest mega city in the world with 42 million people
City planners in south China have laid out an ambitious plan to merge together the nine cities that lie around the Pearl River Delta.
The "Turn The Pearl River Delta Into One" scheme will create a 16,000 sq mile urban area that is 26 times larger geographically than Greater London, or twice the size of Wales.
The new mega-city will cover a large part of China's manufacturing heartland, stretching from Guangzhou to Shenzhen and including Foshan, Dongguan, Zhongshan, Zhuhai, Jiangmen, Huizhou and Zhaoqing. Together, they account for nearly a tenth of the Chinese economy.
Over the next six years, around 150 major infrastructure projects will mesh the transport, energy, water and telecommunications networks of the nine cities together, at a cost of some 2 trillion yuan (£190 billion). An express rail line will also connect the hub with nearby Hong Kong.
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