Miller et al. (1984) presents examples of different images of a pattern of point diffractors obtained by migrating data from various sources and receivers. In particular, they consider combinations of vertical seismic profile (VSP) and surface survey data. Related VSP studies by Kohler and Koenig (1984), Hu and McMechan (1986), Chang and McMechan (1986), and by Sun and McMechan (1986) suggest the importance of multiple offsets for imaging of complicated structures in VSP experiments. The key point is similar to that made by Berkhout (1980), namely, image resolution varies directly with recording aperture. Physically, of course, reconstruction of a structural image by migration can utilize only those waves that were recorded. Partial data produce partial images.