Abstract: The cerebral cortex is composed of neurons with diverse gene expression and long-range projections. Resolving the wiring of diverse neuronal types requires high throughput interrogation of both gene expression and projections at cellular resolution, which is difficult to achieve using conventional techniques. I previously developed BARseq, an in situ sequencing-based technique that can map long-range projections and associate projections with gene expression at cellular resolution and with unprecedented throughput. By further developing in situ sequencing-based neuroanatomical and transcriptomic techniques and deploying them at scale, my team aims to understand the wiring logic of cell types both within and across cortical areas. As a first step, we mapped the spatial distribution of projection neuron types across the whole cortex using BARseq and found surprising differences in area specialization across cell types. This spatial atlas of neuronal types provides a foundation for unraveling the molecular basis for the diversity of cortical projections.