The topography of Mars has been mapped several times by a variety of techniques. We compare the recent Mars Orbiter Laser Altimeter version with the earlier U.S. Geological Survey compilation of photogrammetry and Earth-based radar. We compare them in terms of their respective representations on 1¿¿1¿ grids, though both data sets contain substantially higher spatial resolution. We find that the differences between the two Mars topography models, though locally quite large, are generally quite small. The difference variance is 4% of the data variance. The difference between the two models is also quite notably anisotropic, with substantially more variation north-south than east-west. The variance in the difference between the models is a very small fraction of the data variance at the longest wavelengths and approaches a constant value of ~30% at harmonic degrees above 20. ¿ 2001 American Geophysical Union