(CNN) -- Two years ago, Carlo Ratti, the head of MIT's Senseable City Lab, decided to find out what happened when city residents disposed of trash.
His team recruited 500 volunteers in Seattle to put sensor tags on items they were throwing away, and the researchers tracked the travels of the trash.
Of the 3,000 discarded items that were tracked and visualized in the research, some traveled considerable distances, with one, an ink cartridge, being shipped to the East before winding up in Baja California, a journey of nearly 4,000 miles.
"When you have all these traces of trash moving around," said Ratti, "you can ask yourself how can we make the system more efficient. Then we can make better decisions. And perhaps we will not throw away the plastic bottles that go every day to the dump."
Ratti, a civil engineer and architect, spoke at the TED2011 conference in Long Beach, California, in March and was interviewed by CNN.
"Cities are 2% of the earth's crust but they are 50% of the world's population," and consume 75% of the world's energy, he said.
As computer technology has advanced in past decades, cities have been transformed into digital networks that can be analyzed and activated to improve urban living, Ratti said.
Ratti sees technology as a two-way street. You can use it to make sense of the physical world, digitizing what's out there as he did with the Seattle trash project. But you can also take something that's purely digital and make it real in the physical world.
Among other projects he has worked on was the "Digital Water Pavilion," a building built for an expo in Zaragoza, Spain, with exterior and internal walls produced by flowing water controlled by a computerized system. When you approach the building to enter, sensors stop the water flow to create a doorway you can step through without getting wet.