Based on a new database on positions of the auroral oval boundaries including measurements made by the IMAGE satellite in 2000-2002 with correct determination of the glow boundaries, statistical estimations of the latitudinal position of the polar cap boundary (PCB) are obtained depending on the IMF B_y and B_z, and the PCB evolution during a magnetic storm is analyzed. At zero IMF in the noon (midnight) sector, PCB is located approximately at 80° (76°) CGMLat. The PCB displacement along the noon-midnight meridian is controlled by the IMF B_z, and in the noon (midnight) sector it is equal to 0. 45° (0.15°) CGMLat when B_z changes by 1 nT. The PCB displacement along the dawn-dusk meridian depends on the IMF B_y, and it equals 0. 1° CGMLat when B_y changes by 1 nT. Accordingly, the north polar cap as a whole is shifted to the dawn (dusk) side at B_y > 0 (B_y<0). After northward turn of the IMF during the storm's recovery phase, the PCB on the dayside is shifted to the north practically without time delay. The night boundary requires 25 h or more in order to be shifted to the pole to a latitude corresponding to B_z > 0.