A problem in general relativity is how to extract physical information from solutions to the Einstein equations. Most of the time information is found from specialconditions, e.g., special vector fields, symmetries or approximate symmetries. Our concern is with asymptotically flat space-times with approximate symmetry: the BMS group. For these spaces the Bondi four-momentum vector and its evolution, found at infnity, describes the total energy-momentum and the energy-momentum radiated. By generalizing the simple idea of the transformation of (electromagnetic) dipoles un- der a translation, we fnd the center of mass (center of charge) for asymptotically flat Einstein-Maxwell fields. This gives kinematic meaning to the Bondi four-momentum, i.e., the four-momentum and its evolution is described in terms of a center of mass position vector, its velocity and spin-vector. From dynamic arguments, a unique (for our approximation) total angular momentum and evolution equation in the form of a conservation law is found.