Getting off the ground

LIKE a good Impressionist painting, a city often requires a bit of distance before its viewer can get a feel for the whole picture. Terra, the newest earth-science spacecraft launched by NASA, America's space agency, can provide 700km-worth of distance; and William Stefanov, a geologist at Arizona State University, is using this to develop a better understanding of how people create their cities. At this week's meeting of the American Geophysical Union, in Boston, Dr Stefanov explained how he used data from a satellite-borne instrument called ASTER (Advanced Spaceborne Thermal Emission and Reflection radiometer) to study 12 cities and to classify their growth patterns.