Figure 4. The expression distance metric can be used to search for corresponding cells.

A schematic of the algorithm to identify corresponding cells is shown. For a given query cell, the 30 nearest cells in 3D space in the target embryo are identified. The expression distance between the query cell and each of these target cells is calculated. The best corresponding cell is the target with the lowest expression distance score. This is often not the target cell nearest to the query cell in 3D space.