Yes, Shanghai, one of the most populated cities, is shrinking like a slowly deflated air mattress. The main cause of the sinking is the overuse of underground water. Although the sinking was noticed in 1921, the problem was ignored, and the usage of ground water went on for decades. Recently, Shanghai has switched its water source from well to river to prevent further sinking. However, the effort can only slow the sinking progress. This is because the legacy of Shanghai's severe bouts of ground subsidence. source: abc news