2026ApJS..282...65Y

We present the first data release (DR1) of the Milky Way Imaging Scroll Painting (MWISP) survey, a mapping in the J = 1 → 0 transition lines of ¹²CO, ¹³CO, and C¹⁸O toward the northern Galactic plane during 2011-2022. The MWISP survey was conducted using the Purple Mountain Observatory 13.7 m telescope at a spatial resolution of approximately 50″ and a velocity resolution of 0.16 km s^–1 at 115 GHz. DR1 fully covered 2310 deg² within the Galactic longitude (l) and latitude (b) range of 9$\mathop{.}\limits^{\unicode{x000b0}}$75 ≤ l ≤ 229$\mathop{.}\limits^{\unicode{x000b0}}$75 and ∣b∣ ≤ 5$\mathop{.}\limits^{\unicode{x000b0}}$25. The surveyed area was divided into cell units of $30^{\prime} {\rm{}\,\rm{}}\,\times 30^{\prime} {\rm{}\,\rm{}}\,$ for practical purposes and on-the-fly mapping was performed toward each target cell unit. The data were regridded into a regular three-dimensional data cube in l-b-V_LSR with a pixel size of 30″ in l-b axes and 0.16 km s^–1 in the V_LSR axis. The median rms noise is 0.47, 0.25, and 0.25 K for ¹²CO, ¹³CO, and C¹⁸O, respectively. The equivalent 3σ sensitivity in ¹²CO luminosity is approximately 0.23 K km s^–1, making MWISP the most sensitive survey of its kind. In this paper, we describe the survey data, including the calibration, data cleaning, data mosaic processes, and the data products. The final mosaicked data cubes contain about 3.33 × 10⁷ spectra (pixels) for each CO isotopologue line. Color composite images, made from the intensities of the isotopologue lines, and some concise descriptions are provided. We constructed a molecular cloud catalog based on the mosaicked ¹²CO data cube using the clustering algorithm DBSCAN, detecting 103,517 molecular clouds, 10,790 of which exhibit ¹³CO emission and 304 of which show C¹⁸O emission. Based on the histogram of voxel brightness temperature, we estimated a total ¹²CO flux of 7.69 ± 0.38 × 10⁷ K km s^–1 arcmin², 82% of which is captured by the DBSCAN algorithm. The properties of molecular clouds show a large dynamic range, facilitating more accurate statistics. The data, together with the cloud sample, provide unique information on molecular gas in the northern Milky Way.