During mammalian brain development, relatively few progenitors give rise to a high number of diverse cell types. Temporal regulation is believed to contribute to this diversity; however, it is not sufficient to explain diversity observed between the dorsal pallium and the comparatively understudied lateral and ventral pallium. Now, Frédéric Causeret and colleagues perform single-cell RNA-sequencing in order to understand more about the spatial regulation along the dorso-ventral axis of the pallium. The authors sequence cells of the pallial-subpallial boundary and the surrounding tissues, dissected from E12.5 mice. Using this approach, they reveal that apical progenitors can be described by a gradient of gene expression changes, indicating that progenitor identity changes gradually according to the position of cells along the dorso-ventral axis. In addition, using previously published datasets, the researchers show that progenitor identity results from the superimposition of temporally regulated gene waves that sweep across pallial territories, together with the spatial, stage-invariant gradients. Taken together, these data present new important findings about the link between spatial and temporal diversity of neuronal progenitors in the pallium and provide a fundamental resource for improving our knowledge on cortical neurogenesis.