Column densities of H₂, c-C₃H₂ and CH₃OH extracted along the dotted line present in Fig. 1, as well as the N(H₂) calculated with the model of L1544 described in Keto & Caselli (2010) smoothed at 40′′. While the N(H₂) presents a sharp drop towards the south-west, its decrease is not as steep towards the north-east. The resulting different illumination on the two sides of L1544 is likely to cause the different distribution of cyclopropenylidene and methanol within the core.