Two-dimensional slices related to the EMMA reionisation time field that are smoothed with a Gaussian kernel with a standard deviation of R_f = 6. The top left panel shows t_reion(r) with its minima (black stars). The top right panel shows t_reion(r) with its skeleton (black lines). The bottom left panel shows the isocontours of t_reion(r), with its minima again in black stars. Here, the reionisation time field is normalised to put its mean at a value of 0, and its standard deviation at 1. The bottom right panel shows the norm of the gradient of t_reion(r).