Figure 4 Spatial variation of magnetic parameters, the largest black dot represents the highest value of the corresponding parameters. The areas defined by
black lines are as follows: 1# Lanzhou aluminum plant power and Xigu thermal power plant; 2# Yanerwan, LanDong building materials market enterprise
and leather factory; 3# long and narrow stripe region of materials market-west station-Xiaoxihu Park-Chengguan Bridge; 4# the area surrounding Shuishang
Park.