This vast area of southwest China, the size of France and Spain combined, is famous for its clusters of conical hills, like giant upturned egg cartons, separated by dry empty valleys. This is the karst, a limestone terrain which has become the defining image of southern China. Karst landscapes are often studded with rocky outcrops, forcing local farmers to cultivate tiny fields. The people who live here are among the poorest in China. In neighbouring Yunnan Province, limestone rocks have taken over entirely.