HC₃N(24–23) integrated-intensity map in the velocity range 56– 80 km s^–1. The contour levels are 3, 4, 5, and 6 times the 1σ rms of the map, equal to 1.215 Jy km s^–1. The white star indicates the position of G+0.693 towards which single-dish observations are centred (C1). The white circles show the IRAM 30m and APEX beams at 218.324 GHz (11″ and 27″, respectively), and the maximum beam of the single-dish observations studied in this work, which is 39″ from the Yebes beam at 45.490 GHz (HC₃N(5–4)). The interferometric synthesised beam (474 × 470) is the ellipse indicated in the lower left corner. In the top part, the solid white line indicates the spatial scale of 1 pc.