The first 3-D map of Mars reveals that the planet has some of the highest, lowest and smoothest land forms in the solar system. The map was generated using a laser altimeter aboard NASA's Mars Global Surveyor, which reached Mars in 1997 and began its scientific tasks last year. Surface elevations were determined by firing IR laser pulses and calculating time of flight. The map reveals a surface of extreme highs and lows, with a 20-mile difference between the highest and lowest points. The planet is pear-shaped with a southern hemisphere that is about three miles higher on average than the northern hemisphere. Highlands and basins include features such as a towering volcano and one of the largest craters ever discovered. Scientists constructed the map using 27 million measurements gathered in March and April. The craft continues to collect 900,000 elevation measurements a day.