Here is an excerpt from About Google Mars:
This map of Mars, published by Percival Lowell in 1895, was the result of many years spent carefully studying the Red Planet through his telescope. Now you can do the same through your web browser. In collaboration with NASA"s researchers at Arizona State University, we"ve created some of the most detailed scientific maps of Mars ever made.
If you have half as much fun exploring them as we did making them, you"re in for a great time.
What you are looking at on these maps are Elevation – done in shaded relief map (color coded by altitude), a Visible map taken from the Mars Orbiter Camera, and Infrared images taken by the Thermal Emission Imaging System from NASA"s Mars Odyssey Spacecraft (Shown by Brightness – Darker/Deeper Color Colder – Brighter/Lighter Warmer)
Don"t Forget to check out the Video – The Flight Into Mariner Valley: The Movie