[starky]

This is China's massive differentiator than anywhere else. They have impeccable supply chain management. You will find that certain items are almost always made in the same city. Shenzhen (and surrounding area) is just the hub for electronics manufacturing. Within the city there is the main output, and then a bunch of smaller manufacturers making all the input components within driving distance of that factory which allows it all to work incredibly efficiently. This makes manufacturing in China so much faster than elsewhere.

I'd even go so far to say that Shenzhen is probably the wrong place to build the electric train motor above. I bet there is some 2nd or 3rd tier city somewhere in China that specializes in just that. For example, the only reason I'm aware of the city of Yueqing is because I did a project with pushbuttons once and that is the pushbutton city in China.