In this work we are interested in the global theory of planar quadratic differential systems and more precisely in the geometry of this whole class. We want to clarify some results and methods such as the isocline method or the role of rotation parameters. To this end, we recall how to associate a pencil of isoclines to each quadratic differential equation. We discuss the parameterization of the space of regular pencils of isoclines by the space of its multiple base points and the equivariant action of the affine group on the fibration of the space of regular quadratic differential equations over the space of regular pencils of isoclines. This fibration is principal, with a projective group as structural group, and we prove that there exits an open cone in its Lie algebra whose elements generate rotation parameter families. Finally we use this geometric approach to construct specific families of quadratic differential equations depending in a nonlinear way of parameters wh! ich have a geometric meaning~: they parameterize the set of singular points or are rotation parameters leaving fixed this set.} \keywords{Quadratic systems, pencil of isoclines, rotation parameters