Intensity ratio of J = 3−2 ¹²CO emission in beams of 22″ and 14″ as a function of the effective surface area of the central CO concentration taken from Table 6. Very extended emission has a ratio of unity, and fully unresolved (point-like) sources have a ratio of 2.25. The vertical line corresponds to the surface area of a 14″ beam. The dashed curve indicates the relation expected for circular Gaussian sources without contamination by more extended emission.