Meanwhile, it is possible to partially reconstruct the history of star formation in a region from photometric information, which can provide evolutive classification and the spatial distribution of young sources, and from molecular gas emission maps, which can provide gas distribution and kinematics.

Surveys of GMCs show that embedded star clusters are rarely (if ever) born in isolation. Most embedded clusters form as part of “families" related to a particular complex, defining together a history of star formation from various levels of interaction. For instance, massive stars of one cluster may have influence on the efficiency of star formation of a neighboring cluster in the same cloud. Considering all this, it should be clear that star formation is highly dynamic; the embedded populations we observe are snapshots of a rather convoluted process of evolution and interaction, that changes significantly along the star forming history of a complex.

![image](./f1im.eps){width="6.0in"}

In order to investigate the progression of cluster formation under the influence of the local environment, we considered W3, a prominent cluster forming region in the “Heart and Soul" molecular complex. W3 is considered a clear example of sequential formation, where cluster formation was induced by the expansion of the giant HII 