Comparison of molecular line intensities and tracers of SF. The bottom panel compares the SFR tracers: background-subtracted 24 μm emission and 8 μm emission, also background-subtracted (the background emission is considerably stronger than any stellar contribution at 8 μm). The middle panel shows how the ¹²CO intensity varies with SFR. The top panel shows how the dense gas fraction, as traced by the HCO⁺/CO ratio, varies with SFR. The red triangles indicate the sources which are at high Galactic latitude. It should be immediately apparent that these sources are not distinguishable from the others in the lower two frames but occupy a specific region with low dense gas fraction in the top panel. Neither 8 nor 24 μm data are available for cloud 30.