“Land reclamation” is a fancy way of saying, “building fake land where ocean used to be.” Accordingly, it mostly occurs along coastlines, expanding an existing landmass. Lately, however, China has been using this
technique to create a series of artificial islands the South China Sea.
The secret to China’s success lies in the coral reefs that sit just below sea level throughout the sea. These reefs act as a natural foundation that China can use for its islands: Normally land reclamation requires towing huge stones into the water and then dumping sand on top, but the reefs eliminate the need for towing stones. Instead, China can just haul large amounts of sand over to the reefs, and then dump the sand onto the coral base. This process has let China take drastic leaps forward with land reclamation in the last few years, despite protest from other countries who argue that China is building in disputed territorial waters.
In terms of scope, China has build almost 3,000 acres of new land in just the last 2 years, almost all of which is in the Spratly Islands, a region also claimed in part by Vietnam, Malaysia, Taiwan, and Brunei.
In terms of why China wants to expand, its new islands are useful for real estate development, agriculture, and commerce, as well as (like mentioned above) fortifying its claim to controversial border regions. Other uses for the islands include military outposts for sustaining aircraft carriers, and of course simple urban relief for the country’s growing population.