After three years of intensive data-gathering and careful drawing, the mapmakers’ work was complete.

The complex terrain they charted, with all its peaks, valleys and borders, is only about half an inch long and weighs less than a jellybean: the brain of the laboratory mouse.

In a paper published today in the journal Cell, the Allen Institute mapmakers describe this cartographical feat—the third iteration of the Allen Mouse Brain Common Coordinate Framework, or CCFv3 (https://portal.brain-map.org/), a complete, high-resolution 3D atlas of the mouse brain.