This paper discusses the relationship between x-ray mirror scattering and surface topography using vector electromagnetic scattering theory. The results relate the angular distribution of the scattered intensity to various surface-finish parameters which can, in principle, be determined independently; for example, by x-ray scattering in other geometries, visible-light scattering, or stylus measurements. The key role of spatial band-width limits in such parameters is emphasized. General results are described and illustrated by a discussion of the scattering from isotropically rough surfaces, measured in both a point-detector and in a line-detector geometry. Recent experimental results are then interpreted in terms of the surface-tension model of surface roughness, which predicts a hyperbolic scattering in the line-detector geometry. The present results are offered as a subject for further experimental investigation, a mechanism for predicting the scattering from a given surface, and as a rationale for specifying surface finish in terms of system performance.