Large-scale spatial distribution of our targets (circles) and those of Alcalá et al. (1996, 2000; triangles). Empty symbols refer to low-resolution spectra, while filled symbols represent objects observed at high resolution. The dotted lines mark the strip, the long-dashed line is the Galactic plane, while the dash-dotted lines represent the Gould Belt disk, as outlined by Guillout et al. (1998). The CO J = 1 → 0 emission contour maps by Dame et al. (2001) of the Orion, Monoceros, and Taurus molecular clouds, and the λ Orionis H ii region are also overlaid.