Zhangjiakou, also known as Kalgan and by several other names, is a prefecture-level city in northwestern Hebei province in Northern China, bordering Beijing to the southeast, Inner Mongolia to the north and west, and Shanxi to the southwest. In 2020, its population was 4,118,908 inhabitants, with an area of 36,861.56 square kilometres (14,232.33 sq mi), divided into 17 counties and districts. The built-up area, made of Qiaoxi, Qiaodong, Chongli, Xuanhua, Xiahuayuan Districts, is largely conurbated, with 1,413,861 inhabitants in 2020 in an area of 5,266 km2 (2,033 sq mi). In 2024, the registered population of the whole region is 208.896 million.