china – What is special about the area 30 km west of Beijing?

The map is correct. Beijing literally is there in the east.

Traditionally, Beijing is the dense area, consists of Xicheng and Dongcheng districts, with Forbidden City in the center. Right inside the 2nd Ring Road (二环路). Every Beijing natives and every tourists still call that the city center of Beijing.

But, in 2019, Beijing municipal government moved to Tongzhou 通州 District, a new area specially designed for administration, called “the city’s subsidiary center” (城市副中心).

The Chinese capital has planned for years to shift its administrative
center out to the outer Tongzhou district in an effort to rein in
population growth, traffic congestion and air pollution in Beijing’s
denser inner districts. Caixin report

Maps are taking different display measure. For example, Baidu Map still shows the old city center at low zooming levels, but if zoom in to Tongzhou District, you would see (the Chinese of) Beijing Municipal Government, quite away from Beijing “Proper”:

Baidu map screenshot

Answers about distortion maps are wrong. There is distortion with maps in China, but that is about 100m, not with 30 km.