Wide field near-infrared observations and Spitzer Space Telescope IRAC observations of the DR21/W75 star formation regions are presented .
The photometric data are used to analyse the extinction , stellar content and clustering in the entire region by using standard methods .
A young stellar population is identified all over the observed field , which is found to be distributed in embedded clusters that are surrounded by a distributed halo population extending over a larger projected area .
The Spitzer/IRAC data are used to compute a spectral index value , \alpha , for each YSO in the field .
We use these data to separate pure photospheres from disk excess sources .
We find a small fraction of sources with \alpha in excess of 2 to 3 ( plus a handful with \alpha \sim 4 ) , which is much higher than the values found in the low mass star forming region IC348 ( \alpha \leq 2 ) .
The sources with high values of \alpha spatially coincide with the densest regions of the filaments and also with the sites of massive star formation .
Star formation is found to be occuring in long filaments stretching to few parsecs that are fragmented over a scale of \sim 1 pc .
The spatial distribution of young stars are found to be correlated with the filamentary nebulae that are prominently revealed by 8 \mu m and 850 \mu m observations .
Five filaments are identified that appear to converge on a center that includes the DR21/DR21 ( OH ) regions .
The morphological pattern of filaments and clustering compare well with numerical simulations of star cluster formation by Bate et al .
( 3 ) .