Heavy ion reactions recently are analyzed for fluctuations, which are clearly the dominant sources of azimuthal flow asymmetries in central collisions. In peripheral collisions on the other hand there are azimuthal asymmetries arising from the finite impact parameter and the consequently large angular momentum of the participant system. Experimental results clearly indicate the existence of these two mechanisms in the flow patterns. The talk will discuss how to separate and analyze these two types of flow patterns in peripheral collisions.