Archaeologists have long studied the ancient, crumbling temples of Angkor in Cambodia as sites of worship and gathering. But how Angkor functioned as a city remained unknown.

Now, the airborne laser-scanning technology called lidar has helped fill those gaps, producing maps that reveal remnants of a highly engineered urban landscape hidden beneath a blanket of jungle and rice fields.

“In 20 hours of flying we achieved what may have taken decades of ground surveys,” said Damian Evans, an archaeologist at the University of Sydney in Australia.

Dr. Evans and an international team of researchers analyzed data from about 140 square miles surrounding three ancient Khmer sites: Angkor, Phnom Kulen and Koh Ker. From helicopters, lidar (light detection and ranging) bombards the ground with millions of laser pulses, some of which find their way to the forest floor through gaps in vegetation. It measures the distance between the instrument and the ground, allowing researchers to create high-precision elevation maps.