Want to know where tornadoes have touched down in the United States? Or details about the population density of northern Africa? Check out Map Machine, launched by National Geographic with technical support from ESRI, a leading developer of geographic information system software. The interactive atlas allows users to create maps based on physical, cultural, and weather-related characteristics. Start with a world map that shows the locations of recent earthquakes and then select a particular region to see more closely where the devastation occurred. Users can also search for a particular place (ZIP codes work, too) and ask the virtual cartographer to show its location. Map Machine features electronic versions of atlas maps and country statistics drawn from the latest Atlas of the World. One warning: The site can be sluggish, even with a T1 line, but the maps are well worth the wait.