Median proper motion maps (first column) and corresponding uncertainty maps (second column). The positions of the 50 and 20 km∕s clouds are indicated, along with a region of high μ_l values marked as the ‘ridge’. The white star marks the position of Sgr A^*, and ‘A’ and ‘Q’ denote the Arches and Quintuplet clusters (e.g. Clark et al. 2018; Rui et al. 2019). The ‘F’ marks a region showing higher proper motions than its surroundings, probably due to a dark cloud in front of the CMZ. Colour scales are set independently for the median and uncertainty panels to match the range of their respective values.