An improved rovibrational linelist of formaldehyde, \spec{h212c16o}
Published high-resolution rotation-vibration transitions of \spec{h212c16o}, the principal isotopologue of methanal, are analyzed using the MARVEL (Measured Active Rotation-Vibration Energy Levels) procedure. The literature results are augmented by new, high-accuracy measurements of pure rotational transitions within the ground, $ν_3$, $ν_4$, and $ν_6$ vibrational states. Of the \nbNonRedTr\ non-redundant transitions processed, which come from \nbSr\ sources including the present work, \nbValTr\ could be validated, providing \nbEl\ empirical energy levels of \spec{h212c16o}\ with statistically well-defined uncertainties. All the empirical rotational-vibrational energy levels determined are used to improve the accuracy of ExoMol's AYTY line list for hot formaldehyde. The complete list of collated experimental transitions, the empirical energy levels determined, as well as the extended and improved line list are provided as Supplementary Material.