  The spatial distribution of interactions in high energy collisions of heavy
nuclei is discussed using the wounded nucleon, binary collision, hard sphere,
and colliding disk parameterizations of interaction densities. The mean radius,
its dispersion, and the eccentricity of the interaction region are calculated
as a function of impact parameter. The eccentricity is of special interest for
comparison to measurements of anisotropic flow. The number of participants and
binary collisions is also tabulated as a function of impact parameter.
