Results of the Hessian analysis in the 2° × 2° tiles of the MWISP ¹²CO observations with the maximum (top) and minimum (bottom) values of V, which can be interpreted as a tile dominated by horizontal structures and a tile dominated by vertical structures, respectively. Left: intensity map. Center: map of the eigenvalue of the Hessian matrix identified as λ₋ in Eq. (2), which is used to characterize the filamentary structures in the intensity map. Right: map of the orientation angles evaluated using Eq. (3) after the selections by I and λ₋ introduced in Sect. 2.2.