"Astronomers could one day create rough maps of far-away planets using information taken from starlight reflection, determining the balance of oceans, lands and overhanging clouds."
The process isn't exact. They liken it to trying to figure out what's on a muted TV in another room based on the reflection of the light on the opposite wall.
Below is a test image of Earth from NASA's Deep Impact spacecraft. With the information from the spacecraft, they were able to discern three distinct surface types - land, ocean and cloud.
So we're not going to have a topo map of Gliese 581 c anytime soon, but we might be able to find out a little more about it.
Read the whole article: Live Science: Mapping Distant Planet Surfaces