I've heard somewhere that we have better maps of the surface of Mars than the deepest areas of the sea.
But how accurate are the maps really? Also, how much we have mapped about the surface of Mars?
The highest global coverage of Mars belongs to the THEMIS camera, which has a resolution of 100m per pixel. CTX will likely have global coverage as well, it is currently at 75% coverage, as of April 12, 2012. No doubt this is even higher since then.
The highest resolution from orbit at Mars is the HiRISE camera, at 25 cm/pixel.
Earth's Oceans, for instance, don't have near the resolution. There is an article from 1995 for instance that states that the Ocean Bottom was finally mapped to Venus's resolution, for instance. The best map of the Ocean floor appears to be 100m resolution, with some areas of higher resolution.