Just how big is China?

Everybody who works with Chinese data eventually starts suspecting that GDP is smaller than the official statistics say.  

The video below makes a compelling case that China's GDP may be only 40% of its official size, while also explaining just how China calculates its GDP, and how parlous local government and provincial finances are, and also why it is always a construction boom that is used to stimulate growth out of recession.  By the way, it also hints at why China's municipalities and provinces keep on building unneeded coal power stations.