HNCO (4_0,4–3_0,3) moment 0 maps obtained in the velocity ranges 40–50 km s^–1 (top left panel, the hole), 50–60 km s^–1 (top right panel), 60–70 km s^–1 (bottom left panel, the shell), and 70–80 km s^–1 (bottom right panel, the clump). The contour levels are 0.1 steps from the maximum of the maps (50, 65, 90, and 77 K km s^–1, respectively). The synthesised beam is the ellipse indicated in the lower left corner (2975 × 2975). The white stars are Sgr B2(S), (M), (N), and G+0.693 from the south to the north, and the purple star is the C3 condensation.